Audio Cyclopedia - A highly recommended book
Iain Churches
few people seem to know about the excellent book entitled
Audio Cyclopedia, by Howard Tremaine, who was a designer
at McCurdy Industries, a Canadian company manufacturing
studio and broadcast equipment.
The book, in question and answer format, is comprised of 25 sections,
with more than 1700 pages. The second edition, fourth printing, which
is the edition most often seen, was published in 1975, is mainly tube/valve
orientated but does also have some SS circuits.
Chapters include:
Basic Principles of Sound
Acoustics, Studio techniques.
Microphones,
Attenuators,
Vacuum Tubes, Transistors and Diodes,
Audio Amplifiers,
Disc Recording,
Cutting Heads
Magnetic Recording
Loudspeakers.
Power Supplies,
Test Equipment.
Audio-frequency measurement
Installation
Charts and tables.
I am told by a former colleague from the UK who worked also at
Canadian Broadcasting that the book was one of their training manuals.
Highly recommended!
--
Iain
Patrick Turner
I found a copy in a local technical college library in 1995 and I paid
10c a page to copy
1,000 pages on the photocopier over two days.
The Audio Encyclopedia is a good book, to be sure, and slightly more
modern than RDH4,
but it all mainly obsolete now like most of what is in RDH4 because we
have
developed better ways of achieving good sound in loungerooms
compared to what was done in 1960.
But for anyone whose mind is stuck in the past, and who has unlimited
time
to waste during funded retirement for fixing old junk, the AE is a good
guide.
For myself, its a reference book, and I seldom need to read it now
because I just apply basic known principles to overcome problems and get
on with it.
I have very limited time, and have to earn my money, so I cannot waste
time on junk.
I condensed what I need know and what 95% of other ppl need to know at
my website
for good loungeroom sound.
But for those into cutting LP records or movie track sound et all, and I
don't know anyone at all interested,
and willing to spend the time alone making progress the AE is helpful,
but
one still has to learn what isn't in the books by doing an
apprenticeship.
There are dozens of intersting schematics of commercial circuit designs
in the AE
but I won't ever be using many...
Patrick Turner.
BretLudwig
most common. Unlike the RDH 4, whose price has come down a lot since it
was put up for free, legal download, it is still copyright in the US and
elsewhere so it can't be freely distributed. Furthermore, Tremaine's
family are apparently being prickish and refusing to allow reprint.
Apparently the publishers of "The New Audio Cyclopedia", wished to put a
.pdf of both earlier editions in as a cd-rom with the new one and the
family were impossible to deal with.
CUT COPYRIGHT TERMS TO REASONABLE LENGTH!!!!!!!!
The AC is not primarily about domestic hi-fi and is, like a lot of the old
Audel's and Sams books, written in Q and A format. Nonetheless it is quite
informative as long as one does not expect to be fed and burped and
changed by a book, let alone one dating from 1969.
It is important to remember before slagging old tube equipment that it
was not built to mil spec and was not intended to hold up for 50+ years.
They did not realistically expect anyone in 2008 to give a flying
Philadelphia cream cheese about amplifiers made in 1958. That's true of
American, British, or German equipment, or any other. Whether Quad Leak or
Radford, marantz, McIntosh or Fisher, or Klangfilm or Siemens, it has in
fact held up better than anyone thought it would.
I have several military radios, a Collins S-Line ham receiver and a lot
of old test equipment that was built better, but it cost the price of a
house.
--
Message posted using http://www.talkaboutaudio.com/group/rec.audio.tubes/
More information at http://www.talkaboutaudio.com/faq.html
Engineer
(snip)
> It is important to remember before slagging old tube equipment that it
> was not built to mil spec and was not intended to hold up for 50+ years.
> They did not realistically expect anyone in 2008 to give a flying
> Philadelphia cream cheese about amplifiers made in 1958. That's true of
> American, British, or German equipment, or any other. Whether Quad Leak or
> Radford, marantz, McIntosh or Fisher, or Klangfilm or Siemens, it has in
> fact held up better than anyone thought it would.
>
Agreed, but it can also be "remanufactured" to even better than
original specs (modern caps and resistors) as long as the iron is
good. As long as we can get the tubes it should live "forever"...
well, you know what I mean.
Cheers,
Roger
Iain Churches
"Engineer" <junk...@rogers.com> wrote in message
news:b521583f-22b8-4bbe...@c58g2000hsc.googlegroups.com...
On Jul 29, 12:05 am, "BretLudwig" <bratziru...@gmx.us> wrote:
(snip)
>> It is important to remember before slagging old tube equipment that it
>> was not built to mil spec and was not intended to hold up for 50+ years.
>> They did not realistically expect anyone in 2008 to give a flying
>> Philadelphia cream cheese about amplifiers made in 1958. That's true of
>> American, British, or German equipment, or any other. Whether Quad Leak
>> or
>> Radford, marantz, McIntosh or Fisher, or Klangfilm or Siemens, it has in
>> fact held up better than anyone thought it would.
>>
>Agreed, but it can also be "remanufactured" to even better than
>original specs (modern caps and resistors) as long as the iron is
>good.
Yes- But that's the heart of the problem. Try to find a coil winder
who can make you a transformer *precisely* to the Williamson or
Radford specification. I am, not sure about the situation in the US
but in the EU out of some thirty or so commercial transformer
manufacturers, there seem to be only two that can work to such a high
standard.
Iain
Patrick Turner
But even if the iron is crook, it to can be replaced with better mades.
Its a case of replacing the handle and the blade of dad's old axe,
but the nice box for the axe still has a use.
Patrick Turner.
Patrick Turner
Iain Churches wrote:
>
> "Engineer" <junk...@rogers.com> wrote in message
> news:b521583f-22b8-4bbe...@c58g2000hsc.googlegroups.com...
> On Jul 29, 12:05 am, "BretLudwig" <bratziru...@gmx.us> wrote:
>
> (snip)
>
> >> It is important to remember before slagging old tube equipment that it
> >> was not built to mil spec and was not intended to hold up for 50+ years.
> >> They did not realistically expect anyone in 2008 to give a flying
> >> Philadelphia cream cheese about amplifiers made in 1958. That's true of
> >> American, British, or German equipment, or any other. Whether Quad Leak
> >> or
> >> Radford, marantz, McIntosh or Fisher, or Klangfilm or Siemens, it has in
> >> fact held up better than anyone thought it would.
> >>
>
> >Agreed, but it can also be "remanufactured" to even better than
> >original specs (modern caps and resistors) as long as the iron is
> >good.
>
> Yes- But that's the heart of the problem. Try to find a coil winder
> who can make you a transformer *precisely* to the Williamson or
> Radford specification.
I have demonstrated to myself that doing "*precisely*" what Raddy or
Willy done all those
years ago is a wankerthon.
One does not need vertically divided bobbins for starters.
In most cases, one can improve the design of any given amp made over 20
years ago
by removing all the circuitry and parts and re-doing the whole damn amp
in the manner I have described in many ways at my website.
Most ancient designs of OPT were focused mainly on minimizing copper and
iron
because GOSS and copper had a real price many times what the real price
is now.
Skilled winding tradespeople were both cheap and plentiful in 1958,
so guess what, how did they manage some performance quality without much
iron or copper?
They made special laminations with a larger window area to centre core
area ratio
so more turns could be placed on.
The modern trend is for much lower winding resistances which will
withstand a saturated KT88 indefinately.
Old OPT just heat up and die with shorted turns.
Wiily's OPT had 4,400 P turns of terribly thin fragile wire.
Core was a 44mm stack of 32 tongue material, and window was 75mm x 25mm.
Nowdays one would use 2,200 turns with 60 stack of 51mm tongue to get
saturation
at the same F as in the original Willy OPT at the same voltage applied.
But because the P wire would be so much thicker, and the S wire size,
the OPT
would produce 64W easily at less than 5% winding losses, instead of
Willy's
16W and 10% winding losses.
My website gives an enormous amount of info on how to wind
excellent OPT that will perform better than the Willy models ever did
and which will
be more rugged.
I've never seen the actual winding plans for the Radford amps.
Old secret stuff. Bah, let them keep thie bloody secrets, I don't care,
what I will wind will be better anyway.
> I am, not sure about the situation in the US
> but in the EU out of some thirty or so commercial transformer
> manufacturers, there seem to be only two that can work to such a high
> standard.
Lundahl and Sowter?
I have just nearly completed reforming a VAC 7070 amp with a quad of
300B per channel.
The brand of OPT used is unknown, but they do seem to have a big
simularity
to something made by Hammond, which is the brand used by many
hobbyists in the US and elsewhere.
Hammond ain't the cream though.
It don't matter though, because the VAC OPT do have **enough** bandwidth
to allow
faultless and blameless wonderful sound and technical performance.
So we have a situation where the Hammond is the main choice because its
affordable and good enough.
Something wound like an old Williamson would be 3 times the price, and a
waste of money imho.
If I was a commercial winder, I'd charge twice what Hammond does,
because I know I'd offer a slightly better performance at HF due
to much better interleaving, and better ranges of impedance matches
*without* wasting turns on the secondary.
See my website for details.
Feel free to wind anything you fancy at my website such as OPT No1.
Clever dicks will do a lot better than I have.
Patrick Turner.
>
> Iain
BretLudwig
Lundahl and Sowter?
Patrick Turner."<<
Visit any transformer plant winding stuff under 25 lbs. or so piece
weight, you'll see a largely dickless workforce. Transformer winding is
women's work, quite literally, on a commercial basis.
Patrick Turner
Aha, you know the secret behind secret men's business. Its women.
And indeed they wound many trannies, and made most of the tubes, and
other radio coils
and they did anything that suited their ability for quickly doing
dexterous work repeatedly.
Not many women worked in the design offices afaik.
So that's where the clever dicks were; beavering away to produce good
designs.
In the next office along the corridoor, some bastard called Bean Kownter
laboured away to
dumb down the design to make it use less women's work to wind it.
Its a cunt of a world you know :-)
Patrick Turner.
Iain Churches
"Patrick Turner" <in...@turneraudio.com.au> wrote in message
news:48918BD4...@turneraudio.com.au...
>
> I've never seen the actual winding plans for the Radford amps.
> Old secret stuff. Bah, let them keep thie bloody secrets, I don't care,
> what I will wind will be better anyway.
All good coilwinders are very careful about giving away too
much information. I suppose that's understandable really. It's
their living and they have had to learn what they know the
hard way.
I once talked to Dr. Gavin Sowter about cloning a Radford
OPT. He said, "Hmm, quite a challenge. It is extremely
complex.
In the spec for the STA100 which Radford wrote
for the BBC, he stated, "the amplifier can run
indefinitely at full power into an open or short-circuit
load. I have never seen such a claim from any other
maker!
>
>> I am, not sure about the situation in the US
>> but in the EU out of some thirty or so commercial transformer
>> manufacturers, there seem to be only two that can work to such a high
>> standard.
>
>
> Lundahl and Sowter?
Indeed.
>
> I have just nearly completed reforming a VAC 7070 amp with a quad of
> 300B per channel.
>
> The brand of OPT used is unknown, but they do seem to have a big
> simularity
> to something made by Hammond, which is the brand used by many
> hobbyists in the US and elsewhere.
>
> Hammond ain't the cream though.
They seem to have several different standards of transformers for differing
requirements. A chap I once spoke to at an audio fair, who made
very handsome custom-built Williamsons told me that he had never
been able to make one work properly with a Hammond. I have used
Hammond iron (mainly mains xformers), and found them to be OK,
but their regulation is not as good as the more expensive makers.
> Feel free to wind anything you fancy at my website such as OPT No1.
An acquaintance of mine has been looking for a coilwinding machine for
several years. He come accross all kinds of junk, but never a hig-quality
machine. AVO in the UK used to make one, I think it was marketed
under the name McCade or something similar. It could wind four
bobbins simultaneously. I have never seen one, especially for sale.
I have a feeling that the Radford machines were built in-house. I
rememember on a visit to the Ashton Vale factory seeing three or
four machines.
>
> Clever dicks will do a lot better than I have.
I doubt that many people have enen an inclination to try
Those of use who fettle tube amps have little enough spare time
as it is, without dabbling in the black arts as well:-)
Regards to all
Iain
Patrick Turner
Iain Churches wrote:
>
> "Patrick Turner" <in...@turneraudio.com.au> wrote in message
> news:48918BD4...@turneraudio.com.au...
> >
>
> > I've never seen the actual winding plans for the Radford amps.
> > Old secret stuff. Bah, let them keep thie bloody secrets, I don't care,
> > what I will wind will be better anyway.
>
> All good coilwinders are very careful about giving away too
> much information. I suppose that's understandable really. It's
> their living and they have had to learn what they know the
> hard way.
>
> I once talked to Dr. Gavin Sowter about cloning a Radford
> OPT. He said, "Hmm, quite a challenge. It is extremely
> complex.
Bullshit.
I have heard this bullshit often.
Its all bullshit so the guy can avoid treading on toes, or taking any
time to talk to anyone.
Sowter won't talk to us right here, and what's he worried about?
Is he a snob?
Is he worried that 4 hobbyists will "steal" his ideas during the next 12
mths?
How the fuck are those hobbyists ever going to wind something more
cheaply than
what happens in the Sowter factory?
Radford OPT are just OPT, right?
Follow the golden rules in RDH4, and you get an outcome
at least as good as Radford, or what anyone else can achieve, or better.
My 400W rated OPT in my 300 watt PP amps have 100 stack x 51 core
section, GOSS wasteless.
P = 1,050 turns in 5 sections, two layers each.
Sec has 6 six single layer sections each divided into 24 t + 48 t each
to give a wide range of lossless load matches.
So all up there are 17 windings in my "complex" tranny which isn't very
complex at all.
Because the insulation between P and S = 0.75mm, the Cshunt is low, and
because the interleaving pattern is
6S x 5P, I get 250W bandwidth from 19Hz at saturation to 270kHz, -3dB,
for what is a tranny for 1,200 ohms : 5.6 ohms
with 1,050 : 72 turn ratio.
>
> In the spec for the STA100 which Radford wrote
> for the BBC, he stated, "the amplifier can run
> indefinitely at full power into an open or short-circuit
> load. I have never seen such a claim from any other
> maker!
I have never seen any tube amp able to sustain high levels into a short
circuit.
Of course, the above statement you quote is a lie, and grossly
misleading.
Full PO of 100 watts cannot ever be sustained into an open circuit, or a
short circuit!!!!!
If the load was say 1 ohm, you might get 50W at clipping, not 100W.
But all the amps I have seen which were meant to have 8 ohms connected
will die in the arse
pretty soon if 1 ohm or a short is connected and the input level is left
at the same level as
used to make 100W into 8 ohms.
If you work out the anode dissipation when the amp begins to clip into 1
ohm,
you'll be horrified.
>
> >
> >> I am, not sure about the situation in the US
> >> but in the EU out of some thirty or so commercial transformer
> >> manufacturers, there seem to be only two that can work to such a high
> >> standard.
> >
> >
> > Lundahl and Sowter?
>
> Indeed.
>
> >
> > I have just nearly completed reforming a VAC 7070 amp with a quad of
> > 300B per channel.
> >
> > The brand of OPT used is unknown, but they do seem to have a big
> > simularity
> > to something made by Hammond, which is the brand used by many
> > hobbyists in the US and elsewhere.
> >
> > Hammond ain't the cream though.
>
> They seem to have several different standards of transformers for differing
> requirements. A chap I once spoke to at an audio fair, who made
> very handsome custom-built Williamsons told me that he had never
> been able to make one work properly with a Hammond.
The guy probably had hardly any idea about critical damping.
Hardly anyone does.
I replaced the Chinese OPT in a Jolida 520 with Hammond 1650P and they
worked fine.
The original 520 wasn't very stable. Not much GNFB.
Many Chinese made amps cannot use a high amount of GNFB because their
OPT are so bleedin awful,
and because the makers have no idea about critical damping. Production
is controlled by dumb arse
entrepreneurs, and the marketting ensures hordes of equally dumb arse
customers roll in to spend up big.
Jolida cost over $3,500 in shops here and retail price is at least 20dB
above the cost of production at the sweatshops.
In the 520, I kept the original amount of NFB and stabilised it just
fine.
The Hammond were only marginally better, ie, hardly much better at all
compared to the
original Chinese OPT, one of which had shorted turns on one side of its
vertically divided bobbin.
I pulled the chinese OPT to peices to find the fucked up turns and the
burnt wires.
What a fucking mess i found!!! The ambition of joint venture
American-Chinese management was to make a nice OPT,
but in the making, the fuctard Chinese underpaid overworked cretins in
chinese slave labour sweatshops
failed miserably to maintain quality, and the layers soon became
jumbled, plain insulation tape was used for
P-S insulation, and frankly, the Chinese product was absolute crap.
No real quality control.
With the Hammond, sure, things get fiddly-diddly if you insist on 20dB
GNFB, like Willy did in 1947.
Like the Chinese Jolida OPT, Hammond doesn't use much interleaving in
that particular OPT.
Hammond have released a new range of OPT which entirely avoids having to
adjust
winding connections to get the 4, 8 or 16 ohm outlets. The new range
just has one S winding
with the full S = 16, 0.7 of the winding = 8 ohms, and the CT = 4 ohms,
without the ability
to parallel each 1/2 sec to get low losses and leakage with 4 ohms.
But even ARC use the one S winding suits all approach.
So they have worsened the quality!!!
Why?, because buyers want things simple, and cannot understand anything
even slightly complex any more.
But even with a tranny with 270kHz of BW, you still have troubles with
stability.
The troubles mean oscillation happens at a higher F than it does with an
OPT with a poorer BW.
> I have used
> Hammond iron (mainly mains xformers), and found them to be OK,
> but their regulation is not as good as the more expensive makers.
You pay more for more interleaving less shunt C, less leakage, and
quality.
>
> > Feel free to wind anything you fancy at my website such as OPT No1.
>
> An acquaintance of mine has been looking for a coilwinding machine for
> several years. He come accross all kinds of junk, but never a hig-quality
> machine. AVO in the UK used to make one, I think it was marketed
> under the name McCade or something similar. It could wind four
> bobbins simultaneously. I have never seen one, especially for sale.
I have a friend in Sydney who recently bought a winding lathe made in
Germany
50 years or more ago from an 80 yr old who finally retired.
He says he's able to put on 10,000 turns of fine wire in an ESL step up
tranny
in neat layers before morning tea time. And he never breaks a wire
and it traverses perfectly.
There are winding machines out there.
I couldn't find one either so I made my own.
Its slow, because there isn't any auto traversing mech, but I get a
perfect coil
with persistance.
There is more to making an OPT or PT or choke than just the winding.
There is the designing, the winding, the finding parts, wire, core,
insulations, then
assembly, varnishing, potting, testing and terminations.
There are risks and dangers of fucking up your work at
each and every process.
>
> I have a feeling that the Radford machines were built in-house. I
> rememember on a visit to the Ashton Vale factory seeing three or
> four machines.
> >
> > Clever dicks will do a lot better than I have.
>
> I doubt that many people have enen an inclination to try
> Those of use who fettle tube amps have little enough spare time
> as it is, without dabbling in the black arts as well:-)
OPTs are NOT a black art.
Its just plain simple engineering and trade work that has been mainly
forgotten in western nations as a direct result of using SS which can be
direct coupled to
any load.
The Chinese are now making nearly all the transformers used in western
countries
because the pay rate in China is $2 per day, but in London or Berlin or
new York its $100 per day.
And because workers in the west mainly don't actually work, but sit in
front of screens
and get fat arses.
Everyone who buys chinese goods supports the foul unjust social economic
status quo
where the workers of China are screwed into the dust.
The Chinese are going to try to get rich and in doing so will blacken
the planet with their
soot and the West doesn't want to pay them a fair wage to fund anti CO2
emission measures.
Its a completely fuct up world.
It should be just as economically viable and evironmentally friendly to
set up a factory to anything
in any country, because each worker of the world should get the same pay
for the same work.
Communism couldn't provide that.
Capitalism can't either.
I just wind all my own OPT for my own projects, fuck the rest of the
world; it can do whatever, I don't give a shit.
I also give all my secrets away freely. But they are NOT really MY
secrets, but just common good
knowledge widely known by competent tranny winders of the past, present
and future.
Patrick Turner.
>
> Regards to all
> Iain
Iain Churches
"Patrick Turner" <in...@turneraudio.com.au> wrote in message
news:4892E81A...@turneraudio.com.au...
>
>
> Iain Churches wrote:
>>
>> "Patrick Turner" <in...@turneraudio.com.au> wrote in message
>> news:48918BD4...@turneraudio.com.au...
>> >
>>
>> > I've never seen the actual winding plans for the Radford amps.
>> > Old secret stuff. Bah, let them keep thie bloody secrets, I don't care,
>> > what I will wind will be better anyway.
>>
>> All good coilwinders are very careful about giving away too
>> much information. I suppose that's understandable really. It's
>> their living and they have had to learn what they know the
>> hard way.
>>
>> I once talked to Dr. Gavin Sowter about cloning a Radford
>> OPT. He said, "Hmm, quite a challenge. It is extremely
>> complex.
>
> Bullshit.
> I have heard this bullshit often.
I have dealt with Sowter since the mid 60s, and know many
of the people there personally. BS is not something in which
they indulge.
But, I do remember John Widgery telling me that the Radford
STA100 primary had twenty separate sections in series and
parallel, some with reversed polarity.´That sounds pretty
complex to me!
> Its all bullshit so the guy can avoid treading on toes, or taking any
> time to talk to anyone.
>
> Sowter won't talk to us right here, and what's he worried about?
>
> Is he a snob?
Dr Gavin Sowter ?? A gentleman, but certainly not a snob.
One of the nicest men you could have wished to have met.
He is now in the great transformer winding shop in the sky.
>> In the spec for the STA100 which Radford wrote
>> for the BBC, he stated, "the amplifier can run
>> indefinitely at full power into an open or short-circuit
>> load. I have never seen such a claim from any other
>> maker!
>
> I have never seen any tube amp able to sustain high levels into a short
> circuit.
>
> Of course, the above statement you quote is a lie, and grossly
> misleading.
You can be sure the people at the Beeb amd many others, tried it.
Arthur Radford would have been foolish indeed to make such a
statement if it could be proved to be true. I will try to find the
amp spec and copy it for you.
> Full PO of 100 watts cannot ever be sustained into an open circuit, or a
> short circuit!!!!!
I have such an amplifier, but its value it such that I would be unwilling
to abuse it in any way.
Personally it makes little difference to me either way. I certainly
would not get hot under the collar about it:-)
>
>> > Lundahl and Sowter?
>>
>> Indeed.
>>
>> >
>> > I have just nearly completed reforming a VAC 7070 amp with a quad of
>> > 300B per channel.
>> >
>> A chap I once spoke to at an audio fair, who made
>> very handsome custom-built Williamsons told me that he had never
>> been able to make one work properly with a Hammond.
>
> The guy probably had hardly any idea about critical damping.
>
> Hardly anyone does.
IIRC he mentioned that excess leakage inductance was the problem
with Hammond iron at that time. The situation may or may not have
improved. I cannot say.
Regards to all
Iain
Ian Thompson-Bell
have asked my ocal library to see if they can find me a copy.
There appears to be a modern replacement called The New Audio
Cyclopedia. Is it any good?
Cheers
Ian
Iain Churches
"Ian Thompson-Bell" <ruffr...@yahoo.co.uk> wrote in message
news:g76v2h$bma$1...@energise.enta.net...
> It appears the original Audio Cyclopedia is highly thought of, so I have
> asked my ocal library to see if they can find me a copy.
The second edition was ubiquitous, and used by studios and broadcasting
authorities as a teaching manual. Your library should be able to find you
a copy. I have seen it also in the UK for sale second hand for about
UKP 35
I actually have two copies of the second edition. One of these,
almost mint, I keep by my easy chair in the music room is for
relaxed reading. The other copy is next to my bench. It got left
out in the snow last winter. Don't asky why and how, it's a
long story!!
> There appears to be a modern replacement called The New Audio Cyclopedia.
> Is it any good?
Is this written by Tremaine? Or is it someone trying to cash in
on his reputation ?
The Morgan Jones books are excellent also. I find my second
edition of "Valve Amplifiers" most useful. He also has a book
on the practical aspects of building, called "Building Valve Amplifiers"
One of the chapters is entitled "Metalwork for Poets" ! Morgan Jones
has a first class BBC pedigree, and a very enjoyable writing style.
Iain
Patrick Turner
So bloody what?
20 P sections is NOT especially complex for any OPT.
Usually, some winders say all sorts of crap to ppl to make sure they
think only the
High Priests of Tube Audio are entitled to come up with valid OPT
designs and
be able to wind them properly.
What is usually meant by a "section" isn't something you are familiar
with,
and Widgery did a grand job in pulling wool right over your eyes.
A section of a Primary winding is one that is defined as being all of a
group of turns which are located between
Secondary sections on each side.
So when some buffon say, "Aw gees mate, there are 20 sections that there
primary.."
it implies there would be 21 sections of secondary in a bobbin winding
section with consecutive sections arranged as
SPSPSPSPSPSPSPSPSPSPSPSPSPSPSPSPSPSPSPSPSPS.
This would give the OPT disgustingly high C shunt, and be very poor
practice.
21 P sections when mentioned without definitions that you should have
insisted upon like I would,
could mean that there were 21 primary layers of wire which happens to be
a very common number of P layers.
These layers, you may have discovered had you got the whole truth and
nothing but the truth from Widgery,
might have been divided into say 5 sections if you were lucky, say 4L +
4L + 5L + 4L + 4L,
with the CT for the B+ 1/2 way along the 5L centre section of P.
Its highly likely there are 4 single layer sections of secondary,
perhaps divided into sub sections,
but all very ordinary good practice that i am 100% sure Radford wasn't
going to try to exceed lest he
saddle himself with terrible quality control problems.
But in fact with decent winding machinery and in a mass production
regime, winding complexity
isn't all that difficult if you have the right tradeswomen who've been
well trained after years of
winding all kinds of stuff.
Perhaps the Primary sections of 4 layers each were subdivided into
layers connected "strangly" with regard to winding direction
and sequencing to reduce shunt capacitance.
But Widgery did nothing except deliberatly conceal the truth if indeed
he ever really knew it, and
he bullshitted to boost his ego and aura with the audience that
comprised yourself.
>
> > Its all bullshit so the guy can avoid treading on toes, or taking any
> > time to talk to anyone.
> >
> > Sowter won't talk to us right here, and what's he worried about?
> >
> > Is he a snob?
>
> Dr Gavin Sowter ?? A gentleman, but certainly not a snob.
> One of the nicest men you could have wished to have met.
> He is now in the great transformer winding shop in the sky.
I can't disagree. I never met him, and being dead is a fair excuse for
not being present here.
But we never hear from anyone who IS at Sowter now.
I don't expect them to wade in here because they'd have zero to gain
from the experience.
>
> >> In the spec for the STA100 which Radford wrote
> >> for the BBC, he stated, "the amplifier can run
> >> indefinitely at full power into an open or short-circuit
> >> load. I have never seen such a claim from any other
> >> maker!
> >
> > I have never seen any tube amp able to sustain high levels into a short
> > circuit.
> >
> > Of course, the above statement you quote is a lie, and grossly
> > misleading.
>
> You can be sure the people at the Beeb amd many others, tried it.
> Arthur Radford would have been foolish indeed to make such a
> statement if it could be proved to be true. I will try to find the
> amp spec and copy it for you.
>
> > Full PO of 100 watts cannot ever be sustained into an open circuit, or a
> > short circuit!!!!!
>
> I have such an amplifier, but its value it such that I would be unwilling
> to abuse it in any way.
>
> Personally it makes little difference to me either way. I certainly
> would not get hot under the collar about it:-)
Maybe you see my point.
I am NOT so gullible to believe idiotic claims and half baked
explanations.
If you have an input sine wave equal to that which causes clipping into
8 ohms,
and the outlet has been designed for 8 ohms, then the amp shouldn't
overheat,
ie, Pda should not quite get up to the rating for the tubes, ie, 42
watts for each KT88.
But lemme tellya, if ya run any tube amp with that input voltage, and a
shorted output,
then expect red hot anodes and maybe a fucked OPT within 15 minutes if
the mains fuses don't blow.
Do the calculations for the Pda per KT88, and you'll find the average
tube current x average
tube voltage is way over 42 watts.
Radford amps like all that old stuff do not have active protection, and
rely on fuses.
Sometimes the fuses work when there is gross overload with a sine wave
because the
Idc needing to be supplied to the OPT CT goes way high in a fault
condition.
But it is very easy to blow up many amps with a shorted output with
music, and not have any fuses blow.
Twice last year I repaired a Quad-II amp driving an ESL57 with an
intermittently shorting midrange panel.
Boy whatta mess!
Radford amps would fuck up under the same situation.
> >
> >> > Lundahl and Sowter?
> >>
> >> Indeed.
> >>
> >> >
> >> > I have just nearly completed reforming a VAC 7070 amp with a quad of
> >> > 300B per channel.
> >> >
> >> A chap I once spoke to at an audio fair, who made
> >> very handsome custom-built Williamsons told me that he had never
> >> been able to make one work properly with a Hammond.
> >
> > The guy probably had hardly any idea about critical damping.
> >
> > Hardly anyone does.
>
> IIRC he mentioned that excess leakage inductance was the problem
> with Hammond iron at that time. The situation may or may not have
> improved. I cannot say.
The LL with a 1650P is a bit too high. I know, I used a pair in a Jolida
502 3 mths ago
to replace the horrible Chinese OPTs, one of which had got shorted turns
after 8 years.
The Chinese didn't get the critical damping right, but I did.
Leak made OPT with 50mH of LL and boy they were crap, but you can get
around these defects
if you know how, see my pages on it.
I routinely wind OPT with less than 5mH for the same applications.
Instead of Leaks woeful low amount of interleaving, I use at least a 5S
x 4P section arrangement.
So before you praise up what Radford done, define exactly what he really
did do.
If you asked Leak about his trannies, you'd get all this hogwash about
how fuckin marvellous they were.
But really, Leak OPT were fuckin horrid, and worse than the Chinese
crap.
Sure these things are touted to be "complex" and hard to wind.
BS, most OPT are not complex at all, but the winders always crap on
about their difficulties,
to make themselves look like heroes who should be knighted by QE2.
Some need sending to Siberia to teach them about the truth ahd hard
work.
They talk utter BS and never reveal the REAL details of what they do.
The original Williamson design is one that is defined OPENLY and FREELY
in TRANSPARENT
detail in RDH4 had two side by side indentical bobbins with a lot of
complexity
if that is what it was. Take a look and the simple 1 paragraph
description of it.
Get anything like that paragraph from Widgery?
I rest my case.
John Byrns
"Iain Churches" <Iai...@kolumbus.fi> wrote:
> The Morgan Jones books are excellent also. I find my second
> edition of "Valve Amplifiers" most useful. He also has a book
> on the practical aspects of building, called "Building Valve Amplifiers"
> One of the chapters is entitled "Metalwork for Poets" ! Morgan Jones
> has a first class BBC pedigree, and a very enjoyable writing style.
I find it hard to think positively of Morgan Jones ever since his goof
with the concertina cathode build out resistor in a magazine article and
the first edition of his book. IIRC he flip flopped in the second
edition but he should have known better in the first place. It just
shows that he didn't bother doing the math, which you should do when
making a recommendation that flies in the face of years conventional
practice.
Regards,
John Byrns
--
Regards,
John Byrns
Surf my web pages at, http://fmamradios.com/
Iain Churches
"flipper" <fli...@fish.net> wrote in message
news:c7ke94ht0md68acf0...@4ax.com...
> Could you elaborate on what the goof was?
In the preface to the second edition, Morgan Jones makes a reference
to a number of howlers "for which the author can only humbly aplogize"
Its a 500 page book packed with information, tips, schematics
and formulae. That there were a few errors, now corrected,
is not a surprise.
Most still regard his books as some of the most important in
sustaining the healthy interest in thermionic audio.
Regards to all
Iain
Ian Thompson-Bell
> "Ian Thompson-Bell" <ruffr...@yahoo.co.uk> wrote in message
> news:g76v2h$bma$1...@energise.enta.net...
>
>
>> It appears the original Audio Cyclopedia is highly thought of, so I have
>> asked my ocal library to see if they can find me a copy.
>
> The second edition was ubiquitous, and used by studios and broadcasting
> authorities as a teaching manual. Your library should be able to find you
> a copy. I have seen it also in the UK for sale second hand for about
> UKP 35
>
I checked it out at Amazon and the cheapest I could find was 185USD.
Where in the UK have you seen it for 35 quid?
> I actually have two copies of the second edition. One of these,
> almost mint, I keep by my easy chair in the music room is for
> relaxed reading. The other copy is next to my bench. It got left
> out in the snow last winter. Don't asky why and how, it's a
> long story!!
>
>> There appears to be a modern replacement called The New Audio Cyclopedia.
>> Is it any good?
>
> Is this written by Tremaine? Or is it someone trying to cash in
> on his reputation ?
>
Apparently it includes some of Tremaines work, but is extended to
include more recent stuf e.g.digital. I believe Tremaine is NOT credited
though.
> The Morgan Jones books are excellent also. I find my second
> edition of "Valve Amplifiers" most useful.
Yes, I have that too. Some useful stuff in there not found elsewhere.
He also has a book
> on the practical aspects of building, called "Building Valve Amplifiers"
> One of the chapters is entitled "Metalwork for Poets" ! Morgan Jones
> has a first class BBC pedigree, and a very enjoyable writing style.
>
> Iain
>
Cheers
Ian
>
Iain Churches
"Ian Thompson-Bell" <ruffr...@yahoo.co.uk> wrote in message
news:g77lgo$1k02$1...@energise.enta.net...
> Iain Churches wrote:
>> "Ian Thompson-Bell" <ruffr...@yahoo.co.uk> wrote in message
>> news:g76v2h$bma$1...@energise.enta.net...
>>
>>
>>> It appears the original Audio Cyclopedia is highly thought of, so I have
>>> asked my ocal library to see if they can find me a copy.
>>
>> The second edition was ubiquitous, and used by studios and broadcasting
>> authorities as a teaching manual. Your library should be able to find
>> you
>> a copy. I have seen it also in the UK for sale second hand for about
>> UKP 35
>>
>
> I checked it out at Amazon and the cheapest I could find was 185USD. Where
> in the UK have you seen it for 35 quid?
At a bookshop in Twickenham, just a few months ago.
The mint copy I have is marked £25-95 on the inside cover.
I paid a little more than that for it.
>
>>> There appears to be a modern replacement called The New Audio
>>> Cyclopedia. Is it any good?
>>
>> Is this written by Tremaine? Or is it someone trying to cash in
>> on his reputation ?
>>
>
> Apparently it includes some of Tremaines work, but is extended to include
> more recent stuf e.g.digital. I believe Tremaine is NOT credited though.
Hmm. Curious!
>> The Morgan Jones books are excellent also. I find my second
>> edition of "Valve Amplifiers" most useful.
>
> Yes, I have that too. Some useful stuff in there not found elsewhere.
>
By the way Ian, did you manage to get the Feedback Instruments
phase shift meter you were thinking to bid for on e-Bay?
Regards
Iain
Ian Thompson-Bell
> "Ian Thompson-Bell" <ruffr...@yahoo.co.uk> wrote in message
> news:g77lgo$1k02$1...@energise.enta.net...
>> Iain Churches wrote:
>>> "Ian Thompson-Bell" <ruffr...@yahoo.co.uk> wrote in message
>>> news:g76v2h$bma$1...@energise.enta.net...
>>>
>>>
>>>> It appears the original Audio Cyclopedia is highly thought of, so I have
>>>> asked my ocal library to see if they can find me a copy.
>>> The second edition was ubiquitous, and used by studios and broadcasting
>>> authorities as a teaching manual. Your library should be able to find
>>> you
>>> a copy. I have seen it also in the UK for sale second hand for about
>>> UKP 35
>>>
>> I checked it out at Amazon and the cheapest I could find was 185USD. Where
>> in the UK have you seen it for 35 quid?
>
> At a bookshop in Twickenham, just a few months ago.
> The mint copy I have is marked £25-95 on the inside cover.
> I paid a little more than that for it.
>
Up here in the wilds of Norfolk the only 2nd hand bookshops we have
stock arty farty crap - very little technical stuff and virtually nil
electronics. I visit them regularly but balways come away disappointed.
>>>> There appears to be a modern replacement called The New Audio
>>>> Cyclopedia. Is it any good?
>>> Is this written by Tremaine? Or is it someone trying to cash in
>>> on his reputation ?
>>>
>> Apparently it includes some of Tremaines work, but is extended to include
>> more recent stuf e.g.digital. I believe Tremaine is NOT credited though.
>
> Hmm. Curious!
>
>>> The Morgan Jones books are excellent also. I find my second
>>> edition of "Valve Amplifiers" most useful.
>> Yes, I have that too. Some useful stuff in there not found elsewhere.
>>
>
> By the way Ian, did you manage to get the Feedback Instruments
> phase shift meter you were thinking to bid for on e-Bay?
>
Unfortunately not - had to go out and missed the end of the auction -
wish I had just paid the buy it now price - ah well no matter you can
use the oscillator on its own to measure phase.
Cheers
ian
Iain Churches
"flipper" <fli...@fish.net> wrote in message
news:c5ue94pbjbk9nudt0...@4ax.com...
> I'm not concerned with throwing stones.
No of course not.
> I just wanted to be awares in
> case I run across a site repeating or referencing it.
This book is now into its third edition second or third
printing. The error to which John refers was in the
1st edition, so unless you buy a second hand copy
of the book you will not come across them.
Regards to all
Iain
Patrick Turner
I have a copy of Morgan Jones 'Valve Amplifiers', second edition,
and its riddled with errors and sloppy maths without derivations or
examples or any depth.
Eg, see page 107, with a schematic of a white cathode follower.
Why is the anode R of the top triode = 62k????
It looks like a nice oscillator though
Away from the mistakes, its got some good stuff.
Patrick Turner.
Iain Churches
"Patrick Turner" <in...@turneraudio.com.au> wrote in message
news:4897F0C5...@turneraudio.com.au...
>
> I have a copy of Morgan Jones 'Valve Amplifiers', second edition,
> and its riddled with errors and sloppy maths without derivations or
> examples or any depth.
> Eg, see page 107, with a schematic of a white cathode follower.
> Why is the anode R of the top triode = 62k????
Perhaps this is a misprint? Has it been corected in the 3rd edition
I wonder?
Have you collected together the errors and sent a list of them to
the publishers, for acknowledgement and correction in a future
edition? This would be of greater use to the tube-audio fraternity
that simply denouncing the book here on this group.
>
Iain
Patrick Turner
Sigh, If I was retired, and had all day to do nothing but be "creative"
and not worry about earning money, and not having to interrupt my work
with digging up
drain pipes and repairing /cleaning clogged pipes, and replacing kitchen
plumbing now
46 years old, and doing all this stuff a man has to damn well do besides
be a good tubologist,
then I might get time to properly write a long critique of Mr Jones's
book
which I feel wasn't proofed well enough by himself or anyone else and
then nobody would worry
I was just being grumpy on a news group but then I reckon I have gone
past the age of 40 and have earned the do-as-you-bloody-well-like
license, and now been awarded and official permit from the GOT to be
grumpy, because I cannot do as I like
because the older I get the better I woz.
:-)
Errors bedevil authors severly if they don't re read all their work 10
times slowly, and ask
what a dumb clod would make of what was being written.
I recall writing the last edition of my website over a period of 4
months full time,
and boy, did I make some errors!
Some got past my editediteditediting, and some good ppl
sent me their concerns. There were mainly trivial R or C values, or a
wrong line of calculations.
I fixed the errors as soon as i was told.
I like giving fully worked examples, like RDH4.
People like me who don't believe anything they are told, or anything
they read unless proof is offered,
know how to read books like Jones's.
We have a little chuckle now and then, and move right along, realizing
that nobody, not even ourselves, are perfect.
Patrick Turner.
John Byrns
flipper <fli...@fish.net> wrote:
> On Mon, 04 Aug 2008 10:18:06 -0500, John Byrns <byr...@sbcglobal.net>
> wrote:
>
> Could you elaborate on what the goof was?
The goof was not a typo or an error in a formula, his idea of placing a
build out resistor in the cathode of a concertina phase inverter to
equalize the source impedances of the plate and cathode circuits was
simply a goofy idea. It was a "bright" idea intended to fix an imagined
problem that didn't actually exist, that instead created a real problem.
I saw the magazine article and the first edition of his book where he
presented this goofy idea, I have never seen the second edition of his
book to see how he extricated himself from the predicament he created
for himself, although I have been told by people that have seen the
second edition that he did somehow extricate himself.
Iain Churches
"Patrick Turner" <in...@turneraudio.com.au> wrote in message
news:48986FC0...@turneraudio.com.au...
>
>
> Iain Churches wrote:
>>
>> "Patrick Turner" <in...@turneraudio.com.au> wrote in message
>> news:4897F0C5...@turneraudio.com.au...
>> >
>> > I have a copy of Morgan Jones 'Valve Amplifiers', second edition,
>> > and its riddled with errors and sloppy maths without derivations or
>> > examples or any depth.
>>
>> > Eg, see page 107, with a schematic of a white cathode follower.
>> > Why is the anode R of the top triode = 62k????
>>
>> Perhaps this is a misprint? Has it been corected in the 3rd edition
>> I wonder?
>>
>> Have you collected together the errors and sent a list of them to
>> the publishers, for acknowledgement and correction in a future
>> edition? This would be of greater use to the tube-audio fraternity
>> that simply denouncing the book here on this group.
> Sigh, If I was retired, and had all day to do nothing but be "creative"
> and not worry about earning money, and not having to interrupt my work
> with digging up
> drain pipes and repairing /cleaning clogged pipes, and replacing kitchen
> plumbing now
> 46 years old, and doing all this stuff a man has to damn well do besides
> be a good tubologist,
> then I might get time to properly write a long critique of Mr Jones's
> book
> which I feel wasn't proofed well enough by himself or anyone else and
> then nobody would worry
> I was just being grumpy on a news group but then I reckon I have gone
> past the age of 40 and have earned the do-as-you-bloody-well-like
> license, and now been awarded and official permit from the GOT to be
> grumpy, because I cannot do as I like
> because the older I get the better I woz.
>
> :-)
Understood: And taken in the spirit in which I am sure it
was intended:-)
>
> We have a little chuckle now and then, and move right along, realizing
> that nobody, not even ourselves, are perfect.
>
Erm. Don't you mean "realizing that nobody, not even
ourselves, IS perfect" ?
Cheers:-)
Iain
Iain Churches
"John Byrns" <byr...@sbcglobal.net> wrote in message
news:byrnsj-7A94F3....@newsclstr03.news.prodigy.net...
John, can you get access to the 2nd edition of Valve Amplifiers?
It would be of interest to know if this refers to page 279 of the
paragraph which starts "Output resistance with both terminals
equally loaded" ?
Is not the large difference in output impedance
between anode and cathode an important
shortcoming of the concertina?
Iain
Patrick Turner
Well nobody plus one self would be plural, not singular, because there
are a heck of a lotta nobodies around.
If you had a somebody and you were quite out of your cotton pickin'
mind, then that'd be singular.
Well, single again, after getting unmarried yet again.
Patrick Turner.
>
> Cheers:-)
>
> Iain
Patrick Turner
Not in most amps.
While the loads driven by the CPI remain equal, and nothing clips or
saturates, ie, as in a Williamson amp,
it matters not one bit if one phase is a current source and the other is
a voltage source.
Patrick Turner.
>
> Iain
John Byrns
"Iain Churches" <Iai...@kolumbus.fi> wrote:
Hi Iain,
I no longer have easy access to any of the Morgan Jones magazine
articles or books. The balance of the concertina phase inverter was
extensively discussed here in this group at least once in the past. The
simplest way to look at the balance question is to consider that
ignoring the slight effect caused by the grid to anode and grid to
cathode capacitances the same current flows through both the anode and
cathode circuits, therefore if the cathode and anode loads are made
equal the two output voltages will also be equal since the current in
each is the same.
How does the sentence you quote above, "Output resistance with both
terminals equally loaded", end and what does the next sentence say? I
think most everyone here eventually understood that the concertina was
inherently balanced irrespective of what the output resistances may be.
Relative to the output resistances I think Henry Pasternack and I
disagreed, although the disagreement was not about balance. I took a
conventional view that the two output impedances were different but that
the two output signals ended up equal because the source voltages for
the anode and cathode also differed and exactly compensated for the
differing output impedances, I think I posted all the relevant equations
supporting this view at the time. I basically looked at the anode and
cathode source impedances independently, although you do have to
consider the actual total anode and cathode loads when doing this
analysis.
On the other hand IIRC Henry Pasternack took the view that the anode and
cathode impedances were actually identical in operation because of the
way the signals appear on both the anode an cathode terminals. This
view does sort of workout, but you can't test the anode and cathode
impedances independently, you have to apply equal and opposite test
signals to each when measuring the impedance of either terminal.
> Is not the large difference in output impedance
> between anode and cathode an important
> shortcoming of the concertina?
Yes, the large difference in output impedance is important, but only
when the concertina is driven into clipping, where the dynamically
changing anode and cathode load impedances cause very bizarre clipping
behavior. When the grid of the tube driven from the anode conducts, the
gain at the cathode doesn't change very much, however when the grid of
the tube being driven by the cathode conducts, the gain as seen at the
anode increases very greatly leading to grossly asymmetrical waveforms
at the two outputs. Morgan Jones build out resistor probably helps
moderate this bad clipping behavior, at the expense of balance below
clipping level. I had the impression that his point with the build out
resistor was to equalize the two source impedances so that the high
frequency response would not fall off faster on the anode due to
capacitive loading, although in reality the build out resistor actually
worsens the balance. Perhaps I misunderstood the reason he suggested
the build out resistor and that its real purpose was to mitigate the
poor clipping behavior to some extent. What he actually says in the
second edition may shed some light on what his original intention was.
It would also be interesting to know how he presents the balance issue
in the second edition, does he take the Pasternack or the Byrns approach
to the analysis? My favorite phase inverter is the floating paraphase,
think of it as an inverting opamp in a unity gain configuration.
Patrick Turner
flipper wrote:
> Are you sure about 'nothing clips' in a Williamson?
>
> I mean, with 20dB of NFB, when the output tubes clip the voltage amp
> is going to try going 100 times the drive voltage and I don't see how
> the LTP is going to manage that without going into positive grid drive
> itself.
OK, so the amp begins to clip, so there isn't any increasing NFB signal
sent
to the V1 cathode, so V1 Vgk suddenly begins to increase A times, and
the balanced amp which is already having to make
maybe 40Vrms to drive the OP grids is asked to double that but into OP
tube grid current.
This causes the balanced amp to saturate with its own grid I and the
concertina gets into trouble.
But before the onset of OP tube clipping, the CPI only has to make about
2.5 Vrms to each grid of the
balanced amp, and because there isn't any saturation or clipping of
anything, the CPI
works really well with no strange artifact production.
Si while the OP tubes don't clip in a Wiliamson, none of the 6SN7 input
or driver tubes will.
The Willy amp was designed so that first the OP tubes clip, then the
balanced amp and then the CPI and then input.
The balanced amp in the W act as a buffer against the micro capacitive
FB from OP anodes to the OP grids.
So the CPI sees identical a and k loadings to a very high F.
But eventually capacitance catches up with the CPI, and anode output
falls before the cathode output does.
To ensure equal bandwidth at the CPI a and the k, some small value
trimmer C across the cathode R of the CPI is advisable.
15pF to 47pF is about right, and the value used is chosen to get a
symetrical square wave overshoot at the OPT sec.
The CPI is a stage with a lot of local current NFB, and as such acts as
a buffer between
the input tube and the Miller C of the balanced amp input.
The bandwidth of the Willy input/driver amp with 2 x 6SN7 is over 250kHz
at the OP tube grids, and is damned excellent.
I prefer the use of a single input driving an LTP into one side and with
with common cathode CCS.
Its not quite as "fast" as a Willy amp, but its slightly simpler, and
just as good when NFB is used.
But in some recent re-engineering of ARC and Manley amps, I have used an
input LTP with cathode CCS
to take the input to one grid and NFB to the other, then the output from
this
goes to a second LTP but with a common Rk taken to -120V, and this
worked very well indeed,
with almost no 2H in the distortion character that you get with V1 tube
as an SET.
So it does not matter too much what you use in an input stage and driver
stage
as long as the noise is SFA, bandwidth is over 150kHz for the output
voltage level needed to cause clipping
of the OP stage, and without shelving networks applied,
and distortion is less than 0.5% at the clipping level for the OP tubes,
and the voltage ability
is preferably twice what you need for OP tube clipping before the driver
amp clips itself
without the OP tubes in place; ie loaded by just the bias R cap coupled.
If you can easily satisfy all these design requirements, maybe your
input driver amp is OK.
There are several ways to build a tube amp which has little sonic
signature and
just presents us the music without smear, glare, coldness, hardness, or
damned "tube sound"
with all its faults from compromised engineering.
So, I can repeat this about the CPI, if used wisely,
"it matters not one bit if one phase is a current source and the other
is
a voltage source."
JB and HP had a long running brawl of words about the CPI way back in
2000
when I was told never to mention OPTs or leakage inductance on r.a.t
because it'd lead to a flame war
all over again.
In an ST70, a bootstrapped high gain input pentode must produce slightly
more signal that what
appears at each OP grid.
The CPI between input pentode and OP grids must be able to produce the
OP grid to grid signal,
ie, twice the OP grid signal, and if that was 30Vrms, then the CPI must
make 60Vrms.
When the OP tubes clip and draw grid I then the CPI is immediately in
serious trouble,
and the clipping is asymetrical and ugly.
But so darn what?
The ST70 is a miserly way to build an amplifier; a bean counter special;
something designed by accountants, and to an audiophile, barely
acceptable as entry level gear.
No matter, its purpose is for hi-fi, and the level was never ever meant
to be taken right
up to clipping. Teenagers were never invited to parties, or allowed near
the hi-fi controls
where they immediately press the loudness button, and turn up the bass
boost to max, then run everything
at window breking volume, which includes clipping, and fusing the
tweeters at least.
One of The Best sounding low power amplifiers under 12 watts is made
with a single
12AX7 with 1/2 as an input triode, and 1/2 as a CPI, and the OP tubes
are a pair of EL84 in 40% UL.
15dB GNFB used.
Countless commercial amps like Star etc used this basic recipe.
The EL84/6BQ5 is a very easy tube to drive.
Its a pity that in most integrated chassis where you'll find this
circuit for each channel,
the line stage amp, tone control amp and phono amp are Z grade, noisy,
inaccurate, poor BW, highly distorting
and always degrading the sound well before it hits the power amps.
Mainly because of bean counters trying to use less tubes, less chassis
iron, and less sockets
and less PSU filtering, and generally cheating Joe Public out of what he
paid for.
Patrick Turner.
> >
> >Patrick Turner.
> >>
> >> Iain
tubegarden
> Mainly because of bean counters trying to use less tubes, less chassis
> iron, and less sockets
> and less PSU filtering, and generally cheating Joe Public out of what he
> paid for.
>
> Patrick Turner.
Hi RATs!
We each find something of interest in at least some portion of tube
amps :)
I like hearing what they sound like when I ...
What passes for Audio in the marketplace is very similar to what
passes for sex - in the marketplace.
"Can't buy me love ..."
Money and minds rarely mix ... Bill Gates is not the funniest software
(nor hardware) guy I ever met :)
Enjoy your experiments, they are joys beyond measure, once in a
while ;)
Happy Ears!
Al
Patrick Turner
Hmm, I only get paid if my experiments give the best sound possible.
Sometimes the experiments are painful; they take such a long time and
the pay is very low - Hundreds of hours for just one pair of monoblocs.
In the market place the girls don't love you so the sex is cold and dull
and propelled by illusions.
Good sound must be found after a search for reality without
the chill of dull illusion.
Patrick Turner.
John Byrns
Patrick Turner <in...@turneraudio.com.au> wrote:
> The balanced amp in the W act as a buffer against the micro capacitive
> FB from OP anodes to the OP grids.
> So the CPI sees identical a and k loadings to a very high F.
> But eventually capacitance catches up with the CPI, and anode output
> falls before the cathode output does.
> To ensure equal bandwidth at the CPI a and the k, some small value
> trimmer C across the cathode R of the CPI is advisable.
> 15pF to 47pF is about right, and the value used is chosen to get a
> symetrical square wave overshoot at the OPT sec.
Could you elaborate on this, why it is necessary, is it to compensate
for the effects of the capacitances of the CPI grid?
> JB and HP had a long running brawl of words about the CPI way back in
> 2000
> when I was told never to mention OPTs or leakage inductance on r.a.t
> because it'd lead to a flame war
> all over again.
As I remember it we both agreed that the circuit was basically balanced,
so the brawl must have been over the actual source impedance of the
anode and cathode circuits. Thinking about it over the last 24 hours, I
suspect that what HP was actually measuring/calculating was the source
impedance seen by a load driven as if it were connected between the
anode and cathode, or actually half of that value. I don't believe that
HP's contrived methodology actually demonstrates that the anode and
cathode source impedances are equal as he claimed.
> One of The Best sounding low power amplifiers under 12 watts is made
> with a single
> 12AX7 with 1/2 as an input triode, and 1/2 as a CPI, and the OP tubes
> are a pair of EL84 in 40% UL.
> 15dB GNFB used.
>
> Countless commercial amps like Star etc used this basic recipe.
> The EL84/6BQ5 is a very easy tube to drive.
>
> Its a pity that in most integrated chassis where you'll find this
> circuit for each channel,
> the line stage amp, tone control amp and phono amp are Z grade, noisy,
> inaccurate, poor BW, highly distorting
> and always degrading the sound well before it hits the power amps.
> Mainly because of bean counters trying to use less tubes, less chassis
> iron, and less sockets
> and less PSU filtering, and generally cheating Joe Public out of what he
> paid for.
Surely if the basic pair of EL84s and an ECC83 make a good sounding
power amplifier, there must be a complimentary "bean counter" approved
phono amp and tone control amp to go with it? I assume a "bean counter"
would allow two sockets in each stereo channel to be used in providing
these functions.
John Byrns
flipper <fli...@fish.net> wrote:
> I've seen the classic calculations showing the 'different' anode and
> cathode source impedances, and it sounds logical, but it doesn't
> behave that way.
What do you mean that "it doesn't behave that way", are you saying that
the classic calculations are incorrect?
> I got into checking that with the 13FD7 'mini Williamson' amp because
> I'm using large 'grid stoppers' as a HF roll off so the 'different'
> source impedances became an issue, since they would be 'in series'
> with the grid stopper resistors, but when I spiced it the thing acts
> as if the source impedances are identical. I.E. there is no difference
> in HF roll off (with equal value grid stoppers). To double check I
> also spiced a standalone concertina with just capacitive loading and
> got the same results.
The fact that "there is no difference in HF roll off" doesn't imply that
the anode and cathode source impedances are equal.
> If, however, you accept that the concertina is balanced as long as the
> two loads are equal then it's an 'of course' the roll off is the same
> because the loads are equal, they just vary (equally) with frequency.
The response vs. frequency at the two outputs of the concertina are
balanced, the source impedances are not.
> If you keep the 'different impedance' analysis the thing is as cathode
> impedance drops anode gain increases in exact proportion to the drop
> across the 'larger' anode impedance.
>
> Or, if you use a single common source voltage model (grid), the effect
> of FB is to make the anode and cathode source impedances appear
> equal.
Only HP and you believe that the anode and cathode source impedances
appear equal. The "classic calculations" give the correct results, and
show that the anode and cathode source impedances are not equal, that
does not prevent the two outputs from being balanced when driving equal
loads.
You are ignoring a couple of important points that must be considered
when using the "classic calculations", if you want to get the correct
answer.
First when calculating the source impedance at the cathode you must
include the total anode load in the calculation, this means not just the
plate resistor, but also the coupling capacitor, the following grid
resistor, the shunt and miller capacitances of the following tube, et
al. Similarly when calculating the source impedance at the anode you
must include the total cathode load in the calculations.
Second, it isn't sufficient to calculate only the source impedances, you
must also calculate the source voltages at the anode and cathode.
The trick is that the anode and cathode source voltages vary with
frequency in such a way that they cancel the effects of the differing
source impedances driving the two loads, the result being that the two
output voltages remain balanced even as frequency varies.
> I'm not good enough to do the math but George E. Jones Jr did it in a
> 1951 paper on the subject.
>
> http://www.diybanter.com/attachment.php?attachmentid=3602&d=1213179423
I will take a look at that article, does it come to the conclusion that
the anode and source impedances are equal?
Patrick Turner
John Byrns wrote:
>
> In article <489AC8EF...@turneraudio.com.au>,
> Patrick Turner <in...@turneraudio.com.au> wrote:
>
> > The balanced amp in the W act as a buffer against the micro capacitive
> > FB from OP anodes to the OP grids.
> > So the CPI sees identical a and k loadings to a very high F.
> > But eventually capacitance catches up with the CPI, and anode output
> > falls before the cathode output does.
> > To ensure equal bandwidth at the CPI a and the k, some small value
> > trimmer C across the cathode R of the CPI is advisable.
> > 15pF to 47pF is about right, and the value used is chosen to get a
> > symetrical square wave overshoot at the OPT sec.
>
> Could you elaborate on this, why it is necessary, is it to compensate
> for the effects of the capacitances of the CPI grid?
Its not absoluely necessary. It just makes a prettier looking wave above
50khZ.
But if you ever do measure a Wiliamson type amp, or one with a CPU drive
to the OP tubes,
then you'll see that the HF response of the anode output of the CPI sags
before the cathode.
Some slight C added to the cathode Rk will make the sag even on both
anode and cathode.
The Ren7070 VAC amp I have just re-wired for a guy had 47pF across a 22k
in the CPI.
It also had cross coupled neutralising C from anode connections to the
OPT back to the
oposite grid of the OP 300B. This boosts the HF response with what is
positive FB.
I abolished this utter BS because the amp has selectable amounts of NFB
and
in the 10dB FB selection, there was very lousy HF stability.
But I left the 47pF across the CPI cathode Rk.
>
> > JB and HP had a long running brawl of words about the CPI way back in
> > 2000
> > when I was told never to mention OPTs or leakage inductance on r.a.t
> > because it'd lead to a flame war
> > all over again.
>
> As I remember it we both agreed that the circuit was basically balanced,
> so the brawl must have been over the actual source impedance of the
> anode and cathode circuits.
At the time, you graciously suffered daily broadsides of being called a
complete idiot.
And of course we know you ain't, and Pasternak is nowhere to be seen.
> Thinking about it over the last 24 hours, I
> suspect that what HP was actually measuring/calculating was the source
> impedance seen by a load driven as if it were connected between the
> anode and cathode, or actually half of that value. I don't believe that
> HP's contrived methodology actually demonstrates that the anode and
> cathode source impedances are equal as he claimed.
If you measure the Rout of a CPI SEPARATELY at its anode, its high, and
at the cathode ITS LOW.
but because at AF the load at a and k remain the same, so too does the
balance.
>
> > One of The Best sounding low power amplifiers under 12 watts is made
> > with a single
> > 12AX7 with 1/2 as an input triode, and 1/2 as a CPI, and the OP tubes
> > are a pair of EL84 in 40% UL.
> > 15dB GNFB used.
> >
> > Countless commercial amps like Star etc used this basic recipe.
> > The EL84/6BQ5 is a very easy tube to drive.
> >
> > Its a pity that in most integrated chassis where you'll find this
> > circuit for each channel,
> > the line stage amp, tone control amp and phono amp are Z grade, noisy,
> > inaccurate, poor BW, highly distorting
> > and always degrading the sound well before it hits the power amps.
> > Mainly because of bean counters trying to use less tubes, less chassis
> > iron, and less sockets
> > and less PSU filtering, and generally cheating Joe Public out of what he
> > paid for.
>
> Surely if the basic pair of EL84s and an ECC83 make a good sounding
> power amplifier, there must be a complimentary "bean counter" approved
> phono amp and tone control amp to go with it? I assume a "bean counter"
> would allow two sockets in each stereo channel to be used in providing
> these functions.
You have not had the displeasure to fully examine the woeful attempts by
the army of bean counters
who controlled what the public bought in 1960.
I have, and in nearly every crummy integrated amp, receiver or power +
pre set the
performance left a lot to be desired.
I don't get many sets from 1960 to re-engineer now as I used to 10 years
ago.
Their owners are usually getting old and deaf, and need to be
re-engineered
themselves, just to stay alive.
Most MM phono stages in 1960 consisted of ONE EF86, as in Quad22,
bleedin awful,
or two 1/2 of a 12AX7, which was better IMHO, because there was more NFB
and the response was more
predictable. But most had only nominal adherance to RIAA eq, and actual
responses were
+/- 3dB and different for each channel. Non deleatable tone controls
with similar defects and which
had a passive network driven with 1/2 a 12AX7 were horrid.
Bean counters ensured that only one tube socket and tube was ever to be
used for a single phono channel,
and definately not two sockets and tubes.
Using a ľ-follower stage with a single 12AX7 was utterly out of the
question, and made bean counters
have a fit of apoplexy and foam at the mouth when some innocent young
engineer trotted
into the office with prospective design for next year's models.
It was with great glee that bean counters adopted solid state devices to
replace tubes.
They replaced the music as well with something else.
Patrick Turner.
Patrick Turner
> >The Willy amp was designed so that first the OP tubes clip, then the
> >balanced amp and then the CPI and then input.
>
> You don't want the voltage stages/PS clipping before the OP tubes,
> unless maybe you're making a compressor or intentionally creating
> distortion like in an overdriven guitar preamp or pedal.
You got it.
>
> >The balanced amp in the W act as a buffer against the micro capacitive
> >FB from OP anodes to the OP grids.
> >So the CPI sees identical a and k loadings to a very high F.
> >But eventually capacitance catches up with the CPI, and anode output
> >falls before the cathode output does.
>
> Are you speaking of inter electrode capacitances in the CPI itself or
> the balanced amp grids? Because, if you're speaking of the balanced
> amp grids the roll off is the same despite the seemingly different CPI
> anode/cathode impedances.
The variations in load at the OP tube anodes cause a change in OP tube
gain.
The Miller C varies, so the driver stage experiences a change in load as
well.
If the load on the OP anodes is say low, and then gain is low, so Miller
C is low,
so the load from Miller makes driver stage gain higher.
This might be especially true of a beam tetrode output stage driving
ESL speakers where the C of the speaker means the load goes below 2
ohms, at 18kHz, as in Quad ESL57.
In a W amp, the CPI is largely buffered from the effects of the Miller C
of the OP stage and
the change of gain or change of output balance in the balanced drive amp
would not have a huge effect on the CPI, let alone on the input stage.
> >To ensure equal bandwidth at the CPI a and the k, some small value
> >trimmer C across the cathode R of the CPI is advisable.
> >15pF to 47pF is about right, and the value used is chosen to get a
> >symetrical square wave overshoot at the OPT sec.
> >
> >The CPI is a stage with a lot of local current NFB, and as such acts as
> >a buffer between
> >the input tube and the Miller C of the balanced amp input.
> >The bandwidth of the Willy input/driver amp with 2 x 6SN7 is over 250kHz
> >at the OP tube grids, and is damned excellent.
>
> I didn't say it wasn't 'excellent'. Just said it clips.
> It may not matter with excellent OPTs but with the less than ideal
> OPTs I use CPI clipping can cause HF bursts and the 'excellent'
> bandwidth along with OP triodes makes it more difficult to control
> than a 'plain Jane' CPI into a pair of 6BQ5s. Mainly, I think, because
> that lovely low impedance triode FB more readily shoves the phase
> shifted crap through the OPT.
The low Ra or low driving source resistance of the OP triodes mean that
the the second order filtering effect of the poorer OPT
becomes undamped, and the response is peaked at the sec, has a high
phase shift
and any FB becomes positive all too easily.
Triode OP stage are wonderful sounding things, but have bothers with
damping.
The VAC 7070 I have just worked on is no exception with a quad of 300B
driving an OPT which is no better than a Hammond with regard LL and
Cshunt,
so its very necessary to reduce the OLG of the whole input drive amp
with a Zobel across the V1 anode load, and have a Zobel at the OPT sec,
to get unconditional stability
with 12dB GNFB.
Now I have a pair of Audion horrors to fix.
Same sort of problems.
Un-optimised circuitry, N&D way too high, poor stability.
>
> >JB and HP had a long running brawl of words about the CPI way back in
> >2000
> >when I was told never to mention OPTs or leakage inductance on r.a.t
> >because it'd lead to a flame war
> >all over again.
> >
> >In an ST70, a bootstrapped high gain input pentode must produce slightly
> >more signal that what
> >appears at each OP grid.
> >The CPI between input pentode and OP grids must be able to produce the
> >OP grid to grid signal,
> >ie, twice the OP grid signal, and if that was 30Vrms, then the CPI must
> >make 60Vrms.
> >
> >When the OP tubes clip and draw grid I then the CPI is immediately in
> >serious trouble,
> >and the clipping is asymetrical and ugly.
>
> Yep, if you don't do something about it.
>
> >
> >But so darn what?
>
> Oscillation bursts is potentially what.
Squegging, infact...
>
> >The ST70 is a miserly way to build an amplifier; a bean counter special;
> >something designed by accountants, and to an audiophile, barely
> >acceptable as entry level gear.
> >No matter, its purpose is for hi-fi, and the level was never ever meant
> >to be taken right
> >up to clipping. Teenagers were never invited to parties, or allowed near
> >the hi-fi controls
> >where they immediately press the loudness button, and turn up the bass
> >boost to max, then run everything
> >at window breking volume, which includes clipping, and fusing the
> >tweeters at least.
>
> I hate to ruin your favorite whipping boy but 'bean counters' don't
> 'pick parts' or perform any other design function. They simply 'count
> beans' and tell you the sum.
Bean counters are employed to say no to engineers.
They keep on saying no until the engineers present a design that's
cheaper than the competitors are making.
The engineers go to Confession before Communion,
"Bless me father, for I have Sinned, I sold my fuckin soul to the
Devil..."
" No need to swear my son, three Our Fathers, and six Hail Marys "
And so it was that the people of America were jilted at the shop when
they bought anything.
> >One of The Best sounding low power amplifiers under 12 watts is made
> >with a single
> >12AX7 with 1/2 as an input triode, and 1/2 as a CPI, and the OP tubes
> >are a pair of EL84 in 40% UL.
> >15dB GNFB used.
>
> I wonder what would happen if they tried 20dB of GNFB and are they
> using grid stoppers on the OP tubes?
The grid stoppers don't do a lot in polite hi-fi amps.
Quad-II don't have them between EF86 drivers and KT66 OP tubes.
And really only need to be used to prevent excessive grid currents, or
as a kind of limiter
to prevent rapid rise of bias in the coupling caps on over drive,
something never experienced
in hi-fi listening.
OK, you see them in an Ampeg SVT at 47k per grid of 6550, but the
6550 are in beam tet mode so Miller is low, and there's a high anode
voltage for huge PO levels
and anything can and does happen with guitar amps when driven into heavy
overdrive.
>
> >Countless commercial amps like Star etc used this basic recipe.
> >The EL84/6BQ5 is a very easy tube to drive.
>
> I know. I did the same thing in my 'Stealth AX; amp, except I'm using
> the electrically identical 6GK6..
>
> >Its a pity that in most integrated chassis where you'll find this
> >circuit for each channel,
> >the line stage amp, tone control amp and phono amp are Z grade, noisy,
> >inaccurate, poor BW, highly distorting
> >and always degrading the sound well before it hits the power amps.
> >Mainly because of bean counters trying to use less tubes, less chassis
> >iron, and less sockets
>
> Bean counters count beans, they do not design a damn thing..
>
> >and less PSU filtering, and generally cheating Joe Public out of what he
> >paid for.
>
> In a free market Joe Public gets exactly what he paid for and is free
> to pay more if he wants more.
My point is that he doesn't get what he paid for.
He wants this and that, and reads the sales blurbs, get's fooled into
thinking
the sales blurbs cover what he thought he wanted, and pays out even in
doubt because
its the same sorry story at every brandname.
Excellence was never wasted upon the masses.
There was remarkably good electronics in the moon shot rockets from 1969
onwards,
but it didn't extend to Dynacos and Fords.
Shareholders, CEOs, marketeers, and bean counters all have to get a big
slice of the pie, not leaving
much for Joe Consumer.
Take a packet of chips from the supermarket.
You'd stave to death if that's all you ate, and probably be poisoned.
BS rules, OK.
Its the modern western capitalist way, bloody awful, until you think of
the alternatives.
In 1960, I doubt there was a Russian amplifier that was worth buying,
and there was,
you'd have to wait years for one, or know someone in the Party to get
one,
and it was a similar deal with the "amazingly innovative and economical
Trabant" East German limozine :-) !!!!
Patrick Turner.
>
> >Patrick Turner.
Henry Pasternack
-Henry
moc.ncr@kcanretsaph
John Byrns
flipper <fli...@fish.net> wrote:
> On Fri, 08 Aug 2008 10:11:02 -0500, John Byrns <byr...@sbcglobal.net>
> I explained what I meant in the subsequent text.
>
> >> I got into checking that with the 13FD7 'mini Williamson' amp because
> >> I'm using large 'grid stoppers' as a HF roll off so the 'different'
> >> source impedances became an issue, since they would be 'in series'
> >> with the grid stopper resistors, but when I spiced it the thing acts
> >> as if the source impedances are identical. I.E. there is no difference
> >> in HF roll off (with equal value grid stoppers). To double check I
> >> also spiced a standalone concertina with just capacitive loading and
> >> got the same results.
> >
> >The fact that "there is no difference in HF roll off" doesn't imply that
> >the anode and cathode source impedances are equal.
>
> I think most people would think it implies just that and in most
> circumstances it does. For example, if you're designing an RIAA filter
> you include the source impedance of the driving stage in the
> calculations and if that is 'different' then so would be the
> compensation. Same thing with a guitar tone stack. If you design a
> Marshal style tone stack driven by a low impedance cathode follower
> and then, instead, take from the anode output you get a 'different'
> response because you have a 'different' source impedance.
>
>
> >> If, however, you accept that the concertina is balanced as long as the
> >> two loads are equal then it's an 'of course' the roll off is the same
> >> because the loads are equal, they just vary (equally) with frequency.
> >
> >The response vs. frequency at the two outputs of the concertina are
> >balanced, the source impedances are not.
>
> Makes calculating 1/f=2Pi RC a bitch, don't it?
>
> >> If you keep the 'different impedance' analysis the thing is as cathode
> >> impedance drops anode gain increases in exact proportion to the drop
> >> across the 'larger' anode impedance.
> >>
> >> Or, if you use a single common source voltage model (grid), the effect
> >> of FB is to make the anode and cathode source impedances appear
> >> equal.
> >
> >Only HP and you believe that the anode and cathode source impedances
> >appear equal.
>
> I said no such thing. I talked about both models but made not one
> comment about which I 'believed' or preferred.
>
> A more reasonable interpretation would be that I suggested both views
> are simply different ways of looking at the same thing.
>
> > The "classic calculations" give the correct results, and
> >show that the anode and cathode source impedances are not equal, that
> >does not prevent the two outputs from being balanced when driving equal
> >loads.
> >
> >You are ignoring a couple of important points that must be considered
> >when using the "classic calculations", if you want to get the correct
> >answer.
> >
> >First when calculating the source impedance at the cathode you must
> >include the total anode load in the calculation, this means not just the
> >plate resistor,
>
> I'm not ignoring anything and my referencing the classic equations
> should have given you a clue I'm including all of them.
>
> > but also the coupling capacitor, the following grid
> >resistor, the shunt and miller capacitances of the following tube, et
> >al.
>
> They ain't there in the stand alone CPI test I ran.
>
> Nor does it make any difference to the question at hand because
> they're equal and covered by the caveat of equal load impedances. A
> theorem I verified by running both a 'whole amp' and standalone CPI
> simulation.
>
> > Similarly when calculating the source impedance at the anode you
> >must include the total cathode load in the calculations.
> >
> >Second, it isn't sufficient to calculate only the source impedances, you
> >must also calculate the source voltages at the anode and cathode.
> >
> >The trick is that the anode and cathode source voltages vary with
> >frequency in such a way that they cancel the effects of the differing
> >source impedances driving the two loads, the result being that the two
> >output voltages remain balanced even as frequency varies.
>
> Did you bother to read what I said? Because I said exactly that for
> the 'different impedance' model.
>
> However, the whole point to 'equivalent impedance' calculations is so
> the 'simplified' term can be used in subsequent calculations, like in
> the RIAA filter I mentioned above. But, in the special case of an
> equally loaded CPI, it doesn't provide any useful differentiation
> because, while you can argue all day long that the impedances are
> 'different', there is no difference in the behavior.
>
> As I said, and to which you decided to 'argue' with by saying the same
> thing, the 'trick' is "as cathode impedance drops anode gain increases
> in exact proportion to the drop across the 'larger' anode impedance."
> I.E. the 'source voltages' change.
>
> However, another way to look at it is, with equal load impedances, you
> have a local feedback loop that lowers the 'effective impedance' of
> the anode and that's not a particularly odd view as it's conceivably a
> similar mechanism to that used in lowering amplifier 'effective output
> impedance' with GNFB. Or, conversely (again), if one insists on saying
> the reflected pentode impedance 'is' the (actual) impedance
> (equivalent to arguing the CPI source impedances are, 'in fact',
> different) then the 'source voltage' is changing to compensate for the
> varying load impedance.
>
> The mechanism, in either case, falls apart if the load impedances are
> not the same, like if the following grid goes positive (since they
> don't do so at the same time) and then the 'different' source
> impedances becomes seemingly apparent. Or the feedback loop goes
> cockeyed (as does GNFB at clipping) because the special case it
> depends on is no longer valid.
>
> I say "seemingly" for the 'different impedance' model because, again,
> it does not behave as one would expect from a 'simplified' impedance
> calculation since, when the cathode goes +ve into the following grid,
> the anode signal changes dramatically even though there is no
> 'difference' in the load *it is seeing* (at that point in time). And,
> no, I'm not 'ignoring' that the anode source impedance has changed
> because of the change in cathode impedance, I'm simply saying that
> things fall apart so these 'simplified' equations (calculated for the
> equal load case) no longer hold.
>
>
> >> I'm not good enough to do the math but George E. Jones Jr did it in a
> >> 1951 paper on the subject.
> >>
> >> http://www.diybanter.com/attachment.php?attachmentid=3602&d=1213179423
> >
> >I will take a look at that article, does it come to the conclusion that
> >the anode and source impedances are equal?
>
> He wasn't dealing with that 'argument', although the 'different source
> impedance' model would seem to clearly be what leads people to the
> erroneous 'imbalanced at HF' conclusion, but I suppose it depends on
> how you look at the results. The roll off can be approximated with
> cathode source impedance and the roll off is the same for the plate
> side so one might conclude it has the same effective impedance,
> because that is the apparent behavior.
Flipper, you seem to be flopping all around, trying to walk both sides
of the street, or perhaps trying to swim both sides of the pier would be
more accurate.
The anode and cathode source impedances are either the same or they
aren't the same, you can't have it both ways, you have to pick one or
the other, they can't both be true. Once you have made your choice,
then you can work on trying to justify it.
I still don't see how the fact that the two output voltages remain equal
as the frequency is varied, in anyway implies that the anode and cathode
source impedances are equal?
Of course the effects of grid to anode and grid to cathode capacitance
do unbalance the concertina at very high frequencies, but I leave that
for Patrick to worry about, from my perspective it isn't a problem worth
troubling over.
Patrick Turner
Well, at very HF over say 50kHz, capacitances begin to lower the
way the CPI is loaded at its anode and cathode.
The cathode output tends to have a higher F pole than at the anode.
There us *some* Miller C in the CPI, because the anode
signal is inverted, and effectively, the C between g and a is more than
between g and k.
So the CPI becomes loaded with a lower load at the anode than cathodeand
hence the difference in output levels at HF.
Taken to extreme, consider what happens at 1MHz.
If Cga was say 10pF, ZC = 16k, and so there is the V1 anode Rout in
series with
16k in series with RLa of the CPI triode, and the Cgk is lower, but the
cathode output
is from "follower" action, and anode output falls before cathode output.
The capacitances involved manage to become such low impedances as F
rises they saturate the opeation of the tubes
and the triodes clip. But for ordinary amp builders,
they needn't be too worried and any old CPI works quite well as long as
you don't expect
too much voltage swing or you overload it or expect it to have F2 too
high.
I prefer having an SET input tube using a paralleled twin triode such as
6CG7 or 6DJ8
and then drive an LTP woth a pair of triodes such as two 6CG7 tubes, and
have a CCS cathode sink.
This is best set up so it makes 50% more voltage than needed for output
stage clipping,
and you'll find it overloads symetrically, or at + and - voltage peaks
together.
The Williamson done right sounds just great though.
About the only improvements anyone needs to think about is adding a
small C across the
Rk of the CPI, and then having a long tail resistor from the balanced
amp to say a -120V rail;
about 13k is OK if the Ia in each 1/2 of the balanced amp = 5mA.
This long tail makes the two phases of the balanced driver amp stay
equal
and ensures that much better cancelation of 2H occurs and stops 2H
appearing at each
anode of the balanced amp. The balanced amp creates the most distortion,
and should be a small quantity
of mainly 3H.
Patrick Turner.
John Byrns
flipper <fli...@fish.net> wrote:
> Jokes may be amusing but they're not a valid argument.
It's hard to resist the joke when you're talking to someone who calls
himself "flipper" the "fish". But the point is still valid, you are
trying to have it both ways, which is not physically possible.
> >The anode and cathode source impedances are either the same or they
> >aren't the same, you can't have it both ways, you have to pick one or
> >the other, they can't both be true. Once you have made your choice,
> >then you can work on trying to justify it.
>
> Of course they can 'both be true' because you're talking about
> simplification models, which depend on various assumptions and the
> modeling technique chosen.
How does the fact that we are talking about a "simplification model"
make it possible for the anode source impedance of a concertina to be
both equal to the cathode source impedance and different from it at the
same time and in the same "simplification model"?
> To illustrate lets get to basics.
>
> THEVENIN’S THEOREM
> From the perspective of any load, a linear electric circuit may be
> represented by an ideal voltage source in series with an output
> impedance or resistance.
>
> NORTON’S THEOREM
> From the perspective of any load, a linear electric circuit may be
> represented by an ideal current source in parallel with an output
> impedance or resistance.
>
> OK, so we have two 'different' models that produce the same results so
> which is the 'real' one?
From a modeling perspective they are both the "real one" as you say,
because they both have the same source impedance and equivalent
generator characteristics when viewed from outside the model. When
measuring the source resistance from the outside, as we are doing in the
case of the concertina, it makes no difference which we use inside the
model, there is no way to tell them apart from measurements taken at the
terminals of the model.
Before we get too far from Thevenin and Norton, note that in addition to
a source impedance, they both also include a generator, voltage or
current, which may also have a complex dependence on frequency.
> From the physical world perspective neither are because 'ideal'
> sources do not exist and it's unlikely the thing we're modeling is
> just one resistor. But from a functional perspective, as long as the
> underlying assumptions hold, they 'both' are because they both provide
> a useful model.
Indeed, the source resistance of the concertina anode or cathode isn't
"just one resistor", they are both complex impedances because the load
connected to the other output is a complex impedance, not just a simple
resistor, that is one of several points I have been trying to make.
Using either the Thevenin or the Norton model doesn't restrict us to
"just one resistor" as the source impedance.
> >I still don't see how the fact that the two output voltages remain equal
> >as the frequency is varied, in anyway implies that the anode and cathode
> >source impedances are equal?
>
> Remember, the 'point' to calculating 'effective impedance' is to
> provide something useful for subsequent calculations. So, keeping that
> in mind, we're modeling a black box with a voltage input and two
> outputs, 180 degrees out of phase, that you say have different
> impedances.
Yes, that is correct.
> Those black box outputs are connected to a capacitive load so try
> calculating the RC time constant. Doesn't work that way? Then what's
> the point to the 'effective impedance' calculation?
The point of calculating the effective impedances at the anode and at
the cathode is to allow us to evaluate the effect of unbalanced loads,
in the real world we may not find it convenient to have perfectly
balanced loads, and we may want to evaluate the effects of various
degrees of load imbalance before actually building the circuit.
In the degenerate case of balanced loads the effective RC time constants
at the anode and cathode outputs become equal. There is no real problem
with calculating this single value using the different anode and cathode
source impedances, along with the two generator characteristics.
> Or, conversely, observe that the Cs are equal and the roll off is the
> same. Simple RC implies the impedances out of the black box are equal
> (which answers your question).... but you say they are not.
Correct, the impedances of the two outputs of the black box are not
equal. Everyone seems to agree that an amplifier has different output
impedances from the cathode and anode, yet you and HP expect us to
believe that when we use the amplifier as a concertina the anode and
cathode source impedances suddenly somehow magically become equal! Can
you explain how this transformation takes place?
> You handle this conundrum by jumping inside the black box to explain
> why the 'effective impedance' doesn't do what RC implies. Well, ok, so
> the black box transfer function is a little more complicated, with
> internal 'source voltages' changing under load, but that works.
No, the internal source voltages seen at the anode or at the cathode
don't "change under load" they are fixed in the relatively simple model
we are talking about, just as the source impedances are fixed. It is
important to understand that we are measuring the internal source
voltage at one output at a time, and while this source voltage is
independent of the load applied to the terminal we are measuring at, it
is not independent of the impedance connected to the other output
terminal, just as the source impedance isn't. In other words while the
internal source voltage driving the anode output is independent of the
load connected to the anode terminal, it is not independent of the
impedance connected in the cathode circuit, and vice versa.
> On the other hand, what's wrong with a simple A, -A transfer function
> and equal output impedance model? That gives you the right answer too,
> as long as the underlying equal load impedance assumption is valid.
You have partly answered your own question, the "simple A, -A transfer
function and equal output impedance model" is a very limited model that
only works when the two loads are equal. Why even bother with a model
in that case when a simple inspection of the circuit tells us that the
outputs are equal and opposite when the loads are balanced? The two
output impedance model can tell us what happens when the loads are not
balanced or equal.
The fallacy of HP's argument that the anode and cathode output
impedances are equal is that his method doesn't really measure the anode
and cathode source impedances separately, it really only measures one
source impedance, the one between the anode and cathode terminals. HP
then effectively observes that if the single anode to cathode load is
split into two equal halves, with the center junction grounded,
everything will remain balanced. This contrivance on HPs part in no way
proves that the source impedances at the anode and cathode terminals are
equal, although it is obviously useful in calculating the RC time
constant that you are interested in.
John Byrns
flipper <fli...@fish.net> wrote:
> On Sat, 09 Aug 2008 12:28:58 -0500, John Byrns <byr...@sbcglobal.net>
> wrote:
>
> > But the point is still valid, you are
> > trying to have it both ways, which is not physically possible.
>
> As Jamie on Mythbusters likes to say "well, there's your problem." The
> effective output impedance is not a 'physical' component. It's a model
> and, yes, you can "have it both ways," depending on the model you use,
> just as you can have a current or voltage source, depending on whether
> you use a Thevenin or Norton model.
OK, a model is not the actual physical realization of the concertina,
since you are trying to hide behind the fact that a model is not the
actual physical device let's move on to measuring the actual physical
implementation of the concertina.
Before we do that let me make a few observations about the nature of
models from my perspective. In my world the object of a model is to
duplicate the operation and performance of an actual physical device as
closely as possible, or at least as close as is necessary for the job at
hand. In other words in the case of the concertina the output
impedances of the concertina model should closely approximate those
measured on a physical implementation of the concertina.
From what you have said so far on the subject it is apparent that you
take a completely different approach to modeling, and consider it OK to
build a model that supports a preconceived notion about the device being
modeled, in the case of the concertina that the two output impedances
are equal, rather than actually trying to make the model approximate the
operation of the physical device as closely as possible. My
mathematical model of the concertina was built without any consideration
of what the output impedances might be one way or the other, the output
impedances we only calculated from the model as an after thought without
any preconceived notion of what the results might be.
OK, we have different views on what a model is and how it should be
constructed so let's instead build the real physical thing on a block of
wood and measure the source impedances of the anode and cathode circuits
to see if they are the same or if they are different.
What do you think the results would likely be if we built a physical
concertina, or tapped into one in an existing amp, and measured the
actual source impedances? I suppose the problem with this approach
would be agreeing on a test and measurement protocol to be used in
making the measurements of the source impedances? However if we could
agree on a suitable methodology, measuring the actual physical device
would seem to be a good way to settle the argument once and for all.
Since this equal impedance thing has taken on many of the
characteristics of a myth, perhaps I should submit this problem to the
Mythbusters for a Busted or Confirmed judgment, as my son is a
Mythbusters fanatic.
> I think you've missed the rather astonishing, at the time,
> breakthrough that, regardless of the circuit complexity (and as long
> as the underlying assumptions are met), a linear electric circuit can
> be *modeled* as simply a voltage source (or, later, a current source)
> and one 'equivalent resistor'.
That is rather astonishing, even today, and I did miss it, probably
because it is false. I believe "one equivalent resistor" is incorrect
and it should actually be an impedance not a resistor. I will have to
look it up.
Henry Pasternack
> How does the fact that we are talking about a "simplification model"
> make it possible for the anode source impedance of a concertina to be
> both equal to the cathode source impedance and different from it at the
> same time and in the same "simplification model"?
I've been having an email discussion with Flipper and he seems to be a very
friendly and reasonable guy who certainly hasn't done anything to deserve
such sarcastic and generally difficult treatment by you, John.
There's a simple answer to your question. If you're solving a problem with
a number of variables, and if you don't specify all the variables, the
result
may be a family of solutions that depend on the unspecified variable(s).
This
is a perfectly legitimate outcome.
The inverter is a three-port network. If you measure the output impedance
at one port, you still have to specify what you do with the other ports.
Your
definition of output impedance is a measurement where the opposite output
port is left open-circuited. In the test Flipper and I have proposed, the
opposite output port is terminated in an impedance that always matches the
impedance of the test set.
Your test represents a purely unbalanced load while Flipper's represents a
purely balanced load. The unbalanced test tells us more about how the
inverter performs when the following stage is driven to grid current. The
balanced test tells us more about the case where there is no significant
grid
current. In the first case, the two measured impedances are very
different;
in the other they are the same. There is no contradiction between the two
results because the test conditions are different for each.
An infinite number of other results are possible, depending on how you deal
with the two ports. In this way, you could explore the entire state space
defined by the Preisman equations, and only one model is needed.
On the other hand, as Flipper has said, you might ask if there is a way to
simplify the model so that it changes from a general three-port network into
a pair of two-port networks with their inputs in parallel. This
simplification
is possible, if you impose the constraint of equal loading. And when you do
so, it turns out that not only are the two networks independent, but they
are
also identical. If you can accept the equal load constraint, this is a very
practical and economical solution.
The origin of this discussion, which you have insisted over the years in
turning into an argument, was the question of whether or not some kind of
"build-out" resistor or other hack is needed to equalize the impedances
of the split load inverter. From the very start, I always stated as an
explicit assumption that the two loads were equal. Under that assumption,
and using a well-defined model, the two output impedances are the same.
This is so clear as to be indisputable.
(For that reason, I fully expect you to dispute it.)
If you want to use a more complicated model where the output impedances
aren't equal, then by all means, you're welcome to do so! But please don't
insult those of us who realize we can get the answer we want more easily
by simplifying the model. And watch out for a physicist who comes along
and berates you for the simplifications inherent in your own model.
-Henry
John Byrns
"Henry Pasternack" <f...@bar.com> wrote:
Hi Henry,
I agree that Flipper is friendly and helpful fellow; unfortunately he is
also a very slippery fish who has tried to muddy the waters with his
contention that different models produce different results, effectively
legitimizing any outcome. Without having given a concrete example, this
is just so much BS. For example I believe you and I are using the exact
same model, yet we have come to different conclusions about what the
anode and cathode source impedances of the concertina are. From my
perspective the model is not the issue here, the issue is what we are
measuring, and more importantly how we choose to interpret the results
of those measurements.
The concertina has three output terminals, first the ground or signal
reference terminal, secondly the anode output terminal, and finally the
cathode output terminal. There are three source impedances that can be
measured between two these three terminals. I measured two of these,
the anode to ground source impedance, and the cathode to ground source
impedance. Your method is effectively measuring the source impedance
between the anode and cathode terminals under the assumption that the
concertina and its loads are balanced.
IIRC from a long ago discussion, what you did was to inject equal and
opposite currents into the anode and cathode terminals, and then measure
the voltages developed each of these terminals and the ground terminal.
Normally you would measure the anode to cathode voltage under this
condition to determine the anode to cathode source impedance. I would
suggest that under the conditions that you assumed, namely that the
concertina and its two loads are completely balanced, that the anode and
cathode voltages that you measured are each precisely one half of the
anode to cathode voltage. Hence what you have measured is the anode to
cathode source impedance divided by two, you have not measured equal
source impedances at the anode and cathode.
Your measurement doesn't in any way imply that the anode and cathode
source impedances of the concertina are equal, all you have done is
measure a value that represent one half of the anode to cathode source
impedance under the condition of equal loads.
Given all that, your measurement method is a very clever and useful way
to calculate the RC time constant number that Flipper wants, given the
assumption of complete balance. Your method is far simpler and easier
to apply in that case than my more general method, although in this day
and age of computer spreadsheets the advantage may be somewhat moot.
As far as the issue of reopening this argument goes, I don't believe
that I was the one that did it. I have not gone back to verify exactly
what was said, but I believe it was someone else, probably either
Flipper or Patrick that brought the subject up again. All I did was
mention in response to a discussion about Morgan Jones, and his status
as a guru, that he had got the build out resistor issue wrong. IIRC I
initially justified this only on the basis that the concertina was
already balanced without the build out resistor and that adding the
build out resistor could only serve to unbalance an already balanced
circuit. I do not remember bringing up the argument about source
impedances, as I remember it I simply based my comment on balance. You
will have to look elsewhere for the person that restarted this argument.
As far as I am concerned the whole argument is now moot, since I now
understand how to correctly interpret your measurements, even if you
fail to understand what it was that you actually measured.
John Byrns
flipper <fli...@fish.net> wrote:
> On Sun, 10 Aug 2008 13:32:57 -0500, John Byrns <byr...@sbcglobal.net>
> wrote:
>
> >In article <1cur94l7lnrltu9pg...@4ax.com>,
> > flipper <fli...@fish.net> wrote:
> >
> >> On Sat, 09 Aug 2008 12:28:58 -0500, John Byrns <byr...@sbcglobal.net>
> >> wrote:
> >>
> >> > But the point is still valid, you are
> >> > trying to have it both ways, which is not physically possible.
> >>
> >> As Jamie on Mythbusters likes to say "well, there's your problem." The
> >> effective output impedance is not a 'physical' component. It's a model
> >> and, yes, you can "have it both ways," depending on the model you use,
> >> just as you can have a current or voltage source, depending on whether
> >> you use a Thevenin or Norton model.
>
> Your wholesale elimination of every point made, but two, is disturbing
> because it indicates no argument whatsoever, regardless of it's
> meaning or merit, is going to have any effect. You simply 'wash away'
> whatever is inconvenient.
>
> >OK, a model is not the actual physical realization of the concertina,
>
> It's not just the concertina, A model is a not physical realization.
>
> >since you are trying to hide behind the fact that a model is not the
> >actual physical device
>
> There is no 'hiding'. It's simply what a model 'is' (or is not) and a
> fundamental concept of them.
>
> In even the most trivial Thevenin case, it not only 'is not' a
> physical realization it is flat impossible to make as ideal voltage
> sources simply do not exist. It's an abstraction.
>
> That a model is not a 'real thing', and is developed for a specific
> purpose under defined conditions, is neither trivial nor
> inconsequential. For example, a Thevenin equivalent is intended to
> simulate equivalent output voltage and impedance but it does not
> model power dissipation of the original circuit. So any notion that
> the abstraction is 'real' can lead to erroneous conclusions.
>
> Neither does the Thevenin equivalent work outside defined conditions,
> the most obvious of which being the original circuit operating in it's
> linear region.
>
> I submit it should be obvious that if the intended purpose is
> different, like simulating power in this case, then a different model
> is likely needed.
>
> I further submit that if the defined conditions are different then a
> different model is either likely needed or, at least, possible. In
> fact, one might intentionally limit conditions in order to create a
> simpler model.
>
> Now, all of these models, if done properly, will be valid for the
> intended purpose under the defined conditions despite being quite
> different.
>
> So which is 'real'?
>
> None of them. They're useful abstractions.
>
> > let's move on to measuring the actual physical
> >implementation of the concertina.
>
> Well, we already have one 'measurement' and that's the observation of
> equal roll off, which implies, via the well known RC equation, that
> equal output impendences is a valid model.
>
> You have a different model that also satisfies the observation.
>
> At this point it would probably be a good idea for you to explain what
> it is you're trying to 'prove', or 'convince' me of, because if it's
> that there can be only 'one' model then you've got a serious conflict
> with Thevenin and Norton, and the concept of models in general.
>
> >Before we do that let me make a few observations about the nature of
> >models from my perspective. In my world the object of a model is to
> >duplicate the operation and performance of an actual physical device as
> >closely as possible, or at least as close as is necessary for the job at
> >hand. In other words in the case of the concertina the output
> >impedances of the concertina model should closely approximate those
> >measured on a physical implementation of the concertina.
>
> Fair enough, except to add that, in this context, a model's purpose is
> also to make things simpler and more convenient. I.E., Rather than
> having to analyze the entire original circuit each time one wants to
> see what 'effect' something has one can use the simpler, more
> convenient, model.
>
>
> >From what you have said so far on the subject it is apparent that you
> >take a completely different approach to modeling, and consider it OK to
> >build a model that supports a preconceived notion about the device being
> >modeled, in the case of the concertina that the two output impedances
> >are equal, rather than actually trying to make the model approximate the
> >operation of the physical device as closely as possible. My
> >mathematical model of the concertina was built without any consideration
> >of what the output impedances might be one way or the other, the output
> >impedances we only calculated from the model as an after thought without
> >any preconceived notion of what the results might be.
>
> How in the world do you come up with my contention that both models
> are valid as being a "preconceived notion" favoring one or the other?
>
> On the contrary, even a most casual reading of the preceding
> discussions shows it is you who 'insists' on a particular outcome.
>
>
> >OK, we have different views on what a model is and how it should be
> >constructed so let's instead build the real physical thing on a block of
> >wood and measure the source impedances of the anode and cathode circuits
> >to see if they are the same or if they are different.
> >
> >What do you think the results would likely be if we built a physical
> >concertina, or tapped into one in an existing amp, and measured the
> >actual source impedances?
>
> As I mentioned, one means of measurement has already been done and the
> observation was that the RC time constants appear to be equal. And
> since the Cs are, by definition, equal the common conclusion would
> likely be that the Rs are also equal.
>
> In fact, the 'commonness' of the conclusion, and the common
> understanding of what 'output impedance' means, is what leads people
> to the erroneous conclusion, when using the 'different impedance'
> model,.that the concertina has unequal roll offs.
>
> This is not particularly surprising because the notion is entirely
> consistent with the typical textbook Thevenin equivalent consisting of
> a voltage generator and series 'output impedance'. And one of the
> typical exercises is slapping a capacitor on the output to observe the
> response is a simple Zc, Zo divider because the 'output impedance' is
> Zo..
>
> The text usually explains that this is 'why' the Thevenin is so
> useful, because the behavior of a complex linear circuit and load can
> be reduced to a 'simple' divider equation, and this meaning of 'output
> impedance' is pounded home over and over again.
>
> A concertina befuddles this basic notion because it is not a two
> terminal device and the outputs interact with each other through the
> loads.
>
>
> > I suppose the problem with this approach
> >would be agreeing on a test and measurement protocol to be used in
> >making the measurements of the source impedances?
>
> Could be, because all indications, from the general discussion, are
> you will insist on whichever means 'confirms' what you have already,
> it would seem, decided 'must be' the case.
>
> Might be interesting, though, to see how you intend to measure 'output
> impedance' while maintaining equal loads on the concertina, since that
> is a defined condition.
>
> > However if we could
> >agree on a suitable methodology, measuring the actual physical device
> >would seem to be a good way to settle the argument once and for all.
>
> What 'argument' are you trying to resolve?
>
> >Since this equal impedance thing has taken on many of the
> >characteristics of a myth, perhaps I should submit this problem to the
> >Mythbusters for a Busted or Confirmed judgment, as my son is a
> >Mythbusters fanatic.
>
> Maybe they could deal with the myth there can be only one model.
>
> Or maybe not, because there's nothing to blow up ;)
>
> >> I think you've missed the rather astonishing, at the time,
> >> breakthrough that, regardless of the circuit complexity (and as long
> >> as the underlying assumptions are met), a linear electric circuit can
> >> be *modeled* as simply a voltage source (or, later, a current source)
> >> and one 'equivalent resistor'.
> >
> >That is rather astonishing, even today, and I did miss it, probably
> >because it is false. I believe "one equivalent resistor" is incorrect
> >and it should actually be an impedance not a resistor. I will have to
> >look it up.
>
> I said "at the time" and "at the time" the theorem delft with two
> terminal networks composed of voltage sources, current sources, and
> resistors. The concept was later generalized to impedances.
>
> But in your rush to quibble with non essentials you miss the point,
> which is the concept of modeling and 'equivalent circuits', which are
> (simplified) abstractions of the actual circuit.
>
> That was an astonishing thing, that the 'whole circuit', regardless of
> how complex, could be reduced to just two things, at least for that
> purpose. Granted, none of the things actually exist, and are not
> 'real', but, shazzam, it's a boatload easier to deal with than the
> 'real' one.
Flipper, please see my response to Henry Pasternack for further comment.
Patrick Turner
John Byrns wrote:
>
> In article <1cur94l7lnrltu9pg...@4ax.com>,
> flipper <fli...@fish.net> wrote:
>
> > On Sat, 09 Aug 2008 12:28:58 -0500, John Byrns <byr...@sbcglobal.net>
> > wrote:
> >
> > > But the point is still valid, you are
> > > trying to have it both ways, which is not physically possible.
> >
> > As Jamie on Mythbusters likes to say "well, there's your problem." The
> > effective output impedance is not a 'physical' component. It's a model
> > and, yes, you can "have it both ways," depending on the model you use,
> > just as you can have a current or voltage source, depending on whether
> > you use a Thevenin or Norton model.
>
> OK, a model is not the actual physical realization of the concertina,
> since you are trying to hide behind the fact that a model is not the
> actual physical device let's move on to measuring the actual physical
> implementation of the concertina.
>
> Before we do that let me make a few observations about the nature of
> models from my perspective. In my world the object of a model is to
> duplicate the operation and performance of an actual physical device as
> closely as possible, or at least as close as is necessary for the job at
> hand. In other words in the case of the concertina the output
> impedances of the concertina model should closely approximate those
> measured on a physical implementation of the concertina.
The best model for the triode is the voltage gene producing an output
voltage of
µ x Vg-k, and Ra is a resistance in series between the low Rout gene and
the anode terminal.
So for a typical CPI with 1/2 6SN7, the model becomes a gene with Vo =
20 x Vg-k, and Ra = 10k at typical 4mA of Iadc.
There is say 20k anode load from anode to a fixed 0V point for ac, 20k
cathode load to 0V at ac.
From this its extremely easy to examine what a change in load makes to
the anode voltage or cathode voltage outputs,
and if the loading change is separate to output, or done equally to each
output.
What everone will find is that the Rout at anode is a lot higher than
the Rout at the cathode, if measure separately
and if loaded separately with the same load change to each.
Really basic stuff.
But everyone will find that while the loads stay equal the Vo stays
balanced, until F goes so high and the C
around th circuit begins to unbalance te loadings, and unbalance the
outputs.
With pentodes, most ppl like to use a constant current generator
shunting Ra
for the model of the tube. But one can use µ x Vgk if you want, but then
you get
large imaginery voltages in the model which confuse those with lame
minds.
The CPI has a current output ( high Rout compared to the load) at its
anode,
and voltage output ( low Rout compared to the load) at its cathode,
simple.
Voltage amplitude equality is achieved with local current FB,
and the accuracy of the load match of anode and cathode loads.
>
> > I think you've missed the rather astonishing, at the time,
> > breakthrough that, regardless of the circuit complexity (and as long
> > as the underlying assumptions are met), a linear electric circuit can
> > be *modeled* as simply a voltage source (or, later, a current source)
> > and one 'equivalent resistor'.
>
> That is rather astonishing, even today, and I did miss it, probably
> because it is false. I believe "one equivalent resistor" is incorrect
> and it should actually be an impedance not a resistor. I will have to
> look it up.
The resistor for a load is fine for the tube at AF.
But for above AF, you have to add in the C involved around the whole
circuit,
and then it behaves very differently with impedance loading instead of
just resistive loading.
With CPI, inductance also becomes a factor if F becomes high enough.
Patrick Turner.
Patrick Turner
The apparent paradox which confuses so many about the simple CPI
is the apparent equal Rout at anode or cathode, observed when one
changes the anode and
cathode loads equally.
Since the change of loads causes equal VO to keep appearing, Rout at a
and k must be equal, no?
But they ain't equal at all when measured separately, by changing just
*one* of the TWO loads.
The distinction needs to be remembered about this very simple circuit.
When you add an additional R to the anode to reduce the ohms load, the
voltage sags.
But adding the same R also to the cathode increasess the tube gain with
NFB, and voltage at anode and cathode
become identical if both anode and cathode have the same total RL
connected.
But the addition of the extra RL at anode and cathode *do cause* some
slight
reduction of tube gain and both the anode and cathode voltages fall a
bit, and by the same amount if the load change is equal at a and k.
The *apparent* Rout at and k can be worked out by measuring the VO
change and dividing it by the I change
caused by the additional loading.
I leave you to ponder the math, but its pretty simple.
I doubt I need to work it out, because I know the CPI just works,
and its not a bad way to create two balanced voltages, providing you
don't overload the tube.
The other thing needed to be remembered is that the a and k loads sum to
form the total RL
to determine tube gain without NFB. So 22k plus 22k for 1/2 a 6SN7
make a load of 44k, and the tube gain without FB is 20 x 44k / 54k ( if
µ = 20 and Ra = 10k. )
But with the current FB, tube gain is slightly under two, if one sums
Va&Vk outputs, and divides by Vg.
Patrick Turner.
Henry Pasternack
> As far as I am concerned the whole argument is now moot, since I now
> understand how to correctly interpret your measurements, even if you
> fail to understand what it was that you actually measured.
The argument isn't about circuits at all, since we agree on the behavior,
but rather it's about your unfriendly insistence over the years that I
somehow don't understand what I'm talking about, that I'm "slippery"
and wrong, and so on. And now poor Flipper is caught up in your
web of suspicion as well. LOL!
It seems to me that Flipper is right, and you are so attached to your
idea of what's "real" that you're completely unwilling/unable to see what
the math is telling you. Namely, given the equal load condition (which
has been a stated assumption since day one), the difference between
the two impedances disappears and they become effectively equal.
Yes, the impedance measured from plate to cathode will then be twice
the individual output impedance. This doesn't refute the conclusion,
but follows logically from it given the symmetry of the output voltages.
I've always agreed with you about the impedances being different when
measured separately. But that's irrelevant because there is no way to
perform the measurement you describe without unbalancing the circuit.
And I agree the argument is moot, but not for the reason you think. It's
moot because you insist on violating the equal load constraint, which is
fundamental to my position . So of course you get different results!
When I think of the word "slippery", I have an image of someone
wriggling out of constraints. That's exactly what you're doing, John!
Anyway, I have a very busy week ahead of me, so that's the last I
have to say on the subject. Hopefully, Flipper will take the time to
follow up to your inevitable inane response to this message.
-Henry
This trait of yours to "wriggle" out of constraints really seems to me to
be the essence of "slipperiness." Like your friend (What's his name?
I seem to have forgotten it.) you
Henry Pasternack
news:mbqdnY1B4pgh9T3V...@rcn.net...
> This trait of yours to "wriggle" out of constraints really seems to me to
> be the essence of "slipperiness." Like your friend (What's his name?
> I seem to have forgotten it.) you
Please ignore this left-over text, which I didn't realize was still attached
to the end of my message. FYI, I was going to draw a comparison to
the "slippery" behavior of another r.a.t. participant, but thought better
of it. LOL. Maybe we'll hear from him yet.
-Henry
John Byrns
"Henry Pasternack" <f...@bar.com> wrote:
> "John Byrns" <byr...@sbcglobal.net> wrote in message
> news:byrnsj-0FB809....@newsclstr03.news.prodigy.net...
> > As far as I am concerned the whole argument is now moot, since I now
> > understand how to correctly interpret your measurements, even if you
> > fail to understand what it was that you actually measured.
>
> The argument isn't about circuits at all, since we agree on the behavior,
> but rather it's about your unfriendly insistence over the years that I
> somehow don't understand what I'm talking about, that I'm "slippery"
> and wrong, and so on. And now poor Flipper is caught up in your
> web of suspicion as well. LOL!
Well Flipper has no one to blame but himself for trying to attribute our
differences to different models, when as near as I can tell we are using
essentially the same model, differing only on measurement issues and
their interpretation. Flipper seems to feel that a model can reflect
any result you want, while I feel that a model must be constructed to
mimic the performance of the actual circuit, and that if it doesn't it
isn't a valid model.
> It seems to me that Flipper is right, and you are so attached to your
> idea of what's "real" that you're completely unwilling/unable to see what
> the math is telling you.
I am no more attached to my ideas than you are attached to your ideas
which makes you completely unwilling/unable to see what the math is
telling you.
I will have to look back to see what I said when, however my recent use
of the "idea of what's real" was simply a reaction to Flippers statement
that models weren't physical and therefore could be manipulated to show
whatever you wanted them to show, because models weren't "physical" and
hence didn't represent the truth. As a result I suggested that we build
the actual physical, or "real" circuit and measure that, if the problem
was in the models. Flippers use of the Thevenin and Norton equivalent
circuits as examples in this context is complete nonsense because as
black boxes they are indistinguishable from one another by external
electrical measurements, although you can presumably tell which is
inside the black box by measuring the surface temperature of the box
under open and short circuit conditions.
> Namely, given the equal load condition (which
> has been a stated assumption since day one), the difference between
> the two impedances disappears and they become effectively equal.
And here we have the actual slight of hand, you are talking about a
single impedance, the anode to cathode impedance, not two separate
impedances. You have contrived to make it appear that what you are
measuring two separate impedances, when in reality all you are doing is
measuring the anode to cathode impedance in a questionable way that
gives the appearance that you are actually measuring two separate
impedances when only one impedance is actually being measured. The
customary way to measure impedance is to measure the voltage across the
same two terminals that you are injecting the test current into. In
this case that would mean measuring the voltage between the anode and
cathode terminals, yet you measure between one of those terminals and
ground, a procedure that for an impedance measurement appears completely
bogus on the face of it. Can you cite any support for the measurement
procedure you are using, any suggestion that it is a valid impedance
measurement?
Now because of the symmetry constraint on the circuit it is true that
you are measuring the anode to cathode impedance divided by two. The
actual situation under the balanced load constraint is that the anode to
cathode impedance is driving a load impedance of twice that of either of
the two loads alone, since the two loads are in series and under the
balance constraint, no current will flow between ground and the junction
between the two loads, hence the junction of the two loads can be
disconnected from ground and the loads can be considered to be one
single load of twice the value, driven by the singular anode to cathode
source impedance of the concertina tube.
> Yes, the impedance measured from plate to cathode will then be twice
> the individual output impedance. This doesn't refute the conclusion,
> but follows logically from it given the symmetry of the output voltages.
It sure looks like it refutes the conclusion, because you aren't making
a legitimate impedance measurement, but instead are making a bogus
measurement contrived to prove your point. Under the constrain of
balance it is a useful measurement, but it in no way demonstrates that
the anode and cathode source impedances are equal when the circuit is
balanced, all it demonstrates is that when the circuit is balanced the
single anode to cathode source impedance is effectively driving a load
impedance of twice the magnitude of the individual loads. It does not
in any way demonstrate that the cathode to ground and anode to ground
source impedances are equal.
The bottom line is that what you are measuring is not two quantities
representing the cathode impedance and the anode impedance, but is a
single quantity that is essentially the anode to cathode impedance, this
in no way shows the anode impedance to be equal to the cathode impedance.
> I've always agreed with you about the impedances being different when
> measured separately. But that's irrelevant because there is no way to
> perform the measurement you describe without unbalancing the circuit.
That's quite true, but as I believe I demonstrated some years back, if
you also derive the equations for the voltage generator part of the
Thevenin equivalent circuit, for the anode and cathode circuits, you
will see that your objection falls out in the wash and balanced loads
will see balanced voltages even with the unbalanced source impedances.
> And I agree the argument is moot, but not for the reason you think. It's
> moot because you insist on violating the equal load constraint, which is
> fundamental to my position . So of course you get different results!
How do I violate the equal load constraint? I have always maintained,
and at one time demonstrated, how my method handles the balanced load
condition, how is that "violating the equal load condition"? I also
understand how your method takes advantage of the equal load condition
to provide a simplified calculation. Where is the violation?
What I fail to see is how the fact that your calculation, of what is
effectively the anode to cathode impedance, which provides a useful and
simplified result for the equal load condition, in any way implies that
the anode and cathode source impedances are equal? What you don't seem
to understand is that you are not measuring the anode and cathode source
impedances, but that you are measuring only a single impedance, the
impedance between the anode and cathode.
> When I think of the word "slippery", I have an image of someone
> wriggling out of constraints. That's exactly what you're doing, John!
Tell me again what constraint I am "wriggling" out of, certainly not the
equal load constraint, I have np problem with that?
> Anyway, I have a very busy week ahead of me, so that's the last I
> have to say on the subject. Hopefully, Flipper will take the time to
> follow up to your inevitable inane response to this message.
Perhaps, or perhaps not, but Flipper is plowing a different field
somehow related to different models, not different measurement methods
and interpretations for a single model. If Flipper does respond, it
will be interesting to see where he is going with his different model
theory.
> This trait of yours to "wriggle" out of constraints really seems to me to
> be the essence of "slipperiness." Like your friend (What's his name?
> I seem to have forgotten it.)
I think you must mean Andre, he is doubtlessly thinking you are making a
complete fool of yourself, probably enjoying every minute of it while
making wagers with his friends as to what you will do next.
Henry Pasternack
> [Deleted]
ROTFLMAO!
Enjoy your debate with Flipper, John. :-)
-Henry
John Byrns
flipper <fli...@fish.net> wrote:
> On Mon, 11 Aug 2008 09:48:29 -0500, John Byrns <byr...@sbcglobal.net>
> wrote:
>
> >Flipper, please see my response to Henry Pasternack for further comment.
>
> Maybe. I don't know. But if I do this may be the last time because I'm
> getting a bit tired of putting in a good faith effort only to have you
> flush the whole blooming thing down the toilet.
Hi Flipper,
I'm sorry that I have been ignoring your "good faith effort" and have
been "flushing the whole blooming thing down the toilet" for the moment.
I hope to get back to your comments shortly however my primary interest
in this thread is the source impedance of the anode and cathode
terminals of the concertina phase inverter, whether or not they are
equal, and the interpretation of Henry Pasternack's measurements.
As a result of this focus I have been temporarily fast-forwarding over
any mention of models, especially the mention of the word "model" in
connection with the word "different". Why you might ask have I been
doing this? The reason is simple, it is one of four or five simple
facts that I was going to list in my next post to clarify the context of
this discussion before I drop it and move on to other things, like the
things you have been saying, that I have been fast-forwarding over.
So I will start my contextual list with the first of four or five items.
1. Henry and I are using the same model for the concertina circuit.
At least Henry hasn't said otherwise, and from earlier discussions I
believe it is the case. What does this mean, it means that our models
are not different and hence have little relevance to our disagreement.
The rest of the list will hopefully follow.
Andre Jute
> "Henry Pasternack" <f...@bar.com> wrote:
> > This trait of yours to "wriggle" out of constraints really seems to me to
> > be the essence of "slipperiness." Like your friend (What's his name?
> > I seem to have forgotten it.)
>
> I think you must mean Andre, he is doubtlessly thinking you are making a
> complete fool of yourself, probably enjoying every minute of it while
> making wagers with his friends as to what you will do next.
Poor Old Plodnick is too dull and predictable. Betting on which way a
silkworm will turn on a mulberry leaf is more exciting.
Watching silkworms turn...
Andre Jute
Inventor of the "Ridiculus Curse" (vide Harry Potter, see effects on
Poor Old Plodnick)
Visit Jute on Amps at http://members.lycos.co.uk/fiultra/
John Byrns
flipper <fli...@fish.net> wrote:
> On Mon, 11 Aug 2008 20:34:40 -0500, John Byrns <byr...@sbcglobal.net>
> wrote:
>
> >In article <hch1a4109l5kmj8hc...@4ax.com>,
> > flipper <fli...@fish.net> wrote:
> >
> >> On Mon, 11 Aug 2008 09:48:29 -0500, John Byrns <byr...@sbcglobal.net>
> >> wrote:
> >>
> >> >Flipper, please see my response to Henry Pasternack for further comment.
> >>
> >> Maybe. I don't know. But if I do this may be the last time because I'm
> >> getting a bit tired of putting in a good faith effort only to have you
> >> flush the whole blooming thing down the toilet.
> >
> >Hi Flipper,
> >
> >I'm sorry that I have been ignoring your "good faith effort" and have
> >been "flushing the whole blooming thing down the toilet" for the moment.
> >I hope to get back to your comments shortly however my primary interest
> >in this thread is the source impedance of the anode and cathode
> >terminals of the concertina phase inverter, whether or not they are
> >equal, and the interpretation of Henry Pasternack's measurements.
>
> I take it then you'll be looking for the 'real', 'true', 'actual',
> impedances.
No, that is a game you can play if you are so inclined, I will simply be
looking for the "source" impedance.
> Based on what definition of 'output impedance'?
My definition of "source impedance" should be easy to divine given
comments I have recently made on the subject. I am not wedded to that
definition, although it is congruent with common methods used to measure
the value of resistors and the impedance of other components. Do you
have an alternate definition for the source impedance? I think Terman
wrote a book on electrical measurements, it would be interesting to see
what he might have had to said on the subject, unfortunately I don't
have the book in my library.
> >As a result of this focus I have been temporarily fast-forwarding over
> >any mention of models, especially the mention of the word "model" in
> >connection with the word "different". Why you might ask have I been
> >doing this? The reason is simple, it is one of four or five simple
> >facts that I was going to list in my next post to clarify the context of
> >this discussion before I drop it and move on to other things, like the
> >things you have been saying, that I have been fast-forwarding over.
>
> That's a shame because, judging by the conversation so far, the
> concept of modeling and equivalent circuits is precisely where the
> problem lies.
Given that Henry and I are both using the same model this conclusion
seems illogical to me, however this is precisely the sort of situation
where it is easy to make a logical error. Can you elaborate on why you
say this "is precisely where the problem lies"?
> >So I will start my contextual list with the first of four or five items.
> >
> >1. Henry and I are using the same model for the concertina circuit.
>
> His model has equal output impedances. Yours does not.
No, that is where you have gone off the rails in your thinking. Our
models both have the same source impedances, either equal or not, by
definition since they are the same identical model. The question is a
measurement issue, i.e. who is doing the measurements correctly and who
is doing them incorrectly.
> It's patently obvious they're not the same model.
You keep saying that, please explain the differences between our models.
It would be nice if the models were different because that would offer
the potential for resolving the argument without either of us being
wrong.
However the most satisfying solution would be to abandon the model
entirely, along with the questions it raises, and simply build the
physical circuit and measure the resulting source impedances.
Unfortunately it appears that would just take us back to square one,
again raising the crucial question of how to properly measure the source
impedances.
At this point it appears that the only way to make forward progress
would be to agree on a method for measuring source impedance.
> >At least Henry hasn't said otherwise, and from earlier discussions I
> >believe it is the case. What does this mean, it means that our models
> >are not different and hence have little relevance to our disagreement.
>
> Au contraire.
Again you disagree without providing the slightest discussion of why you
disagree. This is becoming a somewhat irritating personality trait of
yours.
If you think our models are different, it should be a trivial matter for
you to simply point out the differences, as you have not attempted this
simple matter, I can only assume that you are playing a game here, if
that is how you feel so be it.
Patrick Turner
> However the most satisfying solution would be to abandon the model
> entirely, along with the questions it raises, and simply build the
> physical circuit and measure the resulting source impedances.
> Unfortunately it appears that would just take us back to square one,
> again raising the crucial question of how to properly measure the source
> impedances.
Just building something, observing it, measuring it and deciding what is
there
is trifle to complex and real for some around here. They hafta get orf
their bums, and go
into their workshop, and spend time actually doing something.
But ya don't need to all that. Blind Freddy can see that if you measure
the Rout
at the anode by adjusting the anode load and only the anode load, the
Rout
= Vchange / Ichange, which is how you measure the Rout of anything.
If you repeat the same load adjustment to the cathode load and leave the
anode load alone,
you will find Rout is less then at the anode.
And you'll find the cathode is a voltage source, ie, Rout < RL at the
cathode,
and Rout at the anode is a current source, ie, Rout > RL at the anode.
Now this is true of any common cathode amplifier with an unbypassed Rk,
and you test the Rout at
anode and cathode separately.
It would be possible to rig up the CPI so that Rout is the same at a and
k,
but it'd need you to reduce anode RL and increase the cathode RL until
the Rout was the same at a and k.
But then the voltages wouldn't be equal at all, so its not a useful
exercize.
The only way to ensure the CPI has equal Rout at a and k would be to
direct couple
a pair of cathode followers to cathode and anode, and then you'd find
the two Routs would be the same
and each would be equal to what you'd get with any CF.
The theorists here who are making a mountain out of a molehill
could draw up the triode and a voltage gene + Ra resistor as a model in
a CPI with equal anode and cathode loads
and prove to themselves how it all works by working out the voltages and
currents and then moving on to
derive the formulas for Rout at the anode, and Rout at the cathode, in
terms of ľ, Ra, and RL.
>
> At this point it appears that the only way to make forward progress
> would be to agree on a method for measuring source impedance.
I hope I have described a reasonable way to do it.
Measurers will find Rout at cathode a lot less then Rout at anode.
Sorry, but its true.
However, just because the two source resistances are different, it don't
stop the CPI from being a
decent sort of phase inverter, and able to give good enough balance for
most amplifiers
as long as it isn't driven into overload.
I like the CPI as it is in a Williamson better than a Schmitt, or
paraphase
or as in Quad-II, or a transformer.
I am too busy working on tube gear all day long to worry too much about
this
huricane of hot air about CPIs.
Patrick Turner.
Andre Jute
> Blind Freddy can see that if [...]
On RAT when Pasternack gets involved, the question isn't the truth of
an impedance but whether Blind Freddy is congenitally accident-prone
or blinded himself. Adding a conditional "if" to that volatile mix
merely gives the resident weasels another opportunity to perform their
only party trick: weaseling.
Andre Jute
Ah, the human condition! But that would only apply if the subjects
were human. They're not. They're rats.
Patrick Turner
But at least we are not settling issues they way they do in Georgia at
the moment.
I'd be nervous lecturing some Georgians about the benefits of Russian
845 triodes.
It'd depend a bit where you were there because some Georgy boys hate
Ruskies, others love 'em....
Its likely that a couple of big bellied heavies with gold fillings would
wander over to me and shove the 845 *sideways*
up my nether regions.....
I'm also reminded of Churchill's comment about democracy,
"Democracy if bloody terrible, until you think about the alternatives"
So let 'em yabba yabba yabba in the dust for a month about the CPI and
models and things, and nothing will be agreed upon,
and that's how it was 8 years ago over the same damn issue of a
concertina phase inverter, CPI.
The indigenous peoples of Oz have won considerable improvements to their
landrights over the last 25 years.
Now the mining companies actually do have to negotiate the terms of land
use when a new mine is planned.
Talk about yabba yabba! goes on for years before anything is settled,
and until the price
and perks offered meet the indigenies' expectations.
Big holes then get dug, and filled in again.
CPI tube talk gets kinda boring afer awhile; talk about the Consumer
Price Index would be less boring,
unless you lived in Zimbabwee, when the price of bread in the morning
rises 300% by late afternoon, and a wheelbarrow is needed to cart the
price for the loaf.
I hear wheelbarrows have risen 1,000% since yesterday.
I always wonder HTF the Zimbies actually get on, not very well unless
you are among the elete.
But although English is widely spoken there we never hear from audio
experimeters from Zimby
arguing the case about concertinas.
No Africans here afaik, and no Indians. Not even anyone from China.
I live in hope things get more evenly representative on the Internet.
Now I am kicking myself that the Oz dollar has declined from near parity
with the US dollar
and because I should have bought a heafty stock of 6550 etc a month ago.
Its only money though ain't it?
Patrick Turner.
Patrick Turner
flipper wrote:
>
> On Tue, 12 Aug 2008 16:22:18 GMT, Patrick Turner
> <in...@turneraudio.com.au> wrote:
>
> >
> >> However the most satisfying solution would be to abandon the model
> >> entirely, along with the questions it raises, and simply build the
> >> physical circuit and measure the resulting source impedances.
> >> Unfortunately it appears that would just take us back to square one,
> >> again raising the crucial question of how to properly measure the source
> >> impedances.
> >
> >
> >Just building something, observing it, measuring it and deciding what is
> >there
> >is trifle to complex and real for some around here. They hafta get orf
> >their bums, and go
> >into their workshop, and spend time actually doing something.
>
> You get yourself into trouble with those incessant knee jerk snide
> remarks of yours because this matter came up as a result of my doing
> exactly that. I BUILT the damn thing and measured it.
>
> So, with all due respect to you and your bums, sit on it.
OK, Point taken, but some here are arm chair wanabes.
>
> >But ya don't need to all that. Blind Freddy can see that if you measure
> >the Rout
> >at the anode by adjusting the anode load and only the anode load, the
> >Rout
> >= Vchange / Ichange, which is how you measure the Rout of anything.
>
> Not when equal loads is inherent to the circuit and a required
> condition.
But when one talks about the Rout at one point in a circuit,
what is usually meant is that its taken as is at that point,
and without any load adjustments elsewhere.
The Vchange / I change can be used to measure Rout easily for any amp
output.
In the case of the CPI, it can be done if you specifiy that the load
change
to anode and cathode will be equal.
Then the because the same current flows through cathode load, tube, and
anode load,
the Ichange is equal, and because the TWO loads are kept equal, V change
will also be equal,
so you'd think Rout is the same from both terminals.
It is, but subject to conditions.
Unconditionally, its not.
>
> Unequally loaded it isn't a 'concertina' and it doesn't behave like a
> 'concertina'. In fact, measuring your way you'd rip the thing up and
> throw it out because the outputs would be nothing akin to equal and,
> so, of no use as a 'phase inverter'.
Unless you has a pot to lower the higher VO to be equal to the lower VO.
But it wastes gain, so nobody does it.
>
> >If you repeat the same load adjustment to the cathode load and leave the
> >anode load alone,
> >you will find Rout is less then at the anode.
>
> You're not measuring a concertina.
A concertina is merely a normal single ended common cathode triode amp
stage, but one with
a cathode resistor equal to the anode resistor.
So when measuring a concertina, you are measuring a common cathode
amplifier stage.
>
> >And you'll find the cathode is a voltage source, ie, Rout < RL at the
> >cathode,
> >and Rout at the anode is a current source, ie, Rout > RL at the anode.
>
> You're not measuring a concertina.
>
> >Now this is true of any common cathode amplifier with an unbypassed Rk,
> >and you test the Rout at
> >anode and cathode separately.
>
> That's right, a common cathode amplifier, not a concertina.
As I said, a concertina *is* a common cathode amp......
The word concertina is used so everyone knows the cathode load = anode
load,
hence Va = Vk.
>
> >It would be possible to rig up the CPI so that Rout is the same at a and
> >k,
> >but it'd need you to reduce anode RL and increase the cathode RL until
> >the Rout was the same at a and k.
> >But then the voltages wouldn't be equal at all, so its not a useful
> >exercize.
>
> Nope, because if one defines 'output impedance' per the Thevenin model
> then a concertina already has equal Thevenin 'output impedances' as
> long as the loads are equal.
If measured separately, you get what ya get, if measured conditioanlly,
you get something else, a convenient measure.
I have never worked out exactly what the conditional Rout of the
CPI actually is. But its somewhere higher than a cathode folower, and
lower than from
a normal common cathode amp at its anode and with fully bypassed
cathode.
Math experts should have come up with all the releveant figures by now,
but I've never
*needed* to calculate the Rout, so I have never have.
>
> >The only way to ensure the CPI has equal Rout at a and k would be to
> >direct couple
> >a pair of cathode followers to cathode and anode, and then you'd find
> >the two Routs would be the same
> >and each would be equal to what you'd get with any CF.
>
> There is no need because if one defines 'output impedance' per the
> Thevenin model then a concertina already has equal Thevenin 'output
> impedances' as long as the loads are equal.
"as long as the loads are equal" is the condition needed for equal Rout
at each terminal.
What if they were not in a dynamic working amp?
This becomes a fact when a CPI runs into grid current powering output
tubes.
The grid current affects the anode signal supply far more than the
cathode supply,
and the amp clipping becomes grossly asymetrical, ie, like a dogs'
breakfast,
with gross asymetrical dc offsets. So in guitar amps, 99% use a
balanced amp or LTP to drive the output stage which gives symetrical
clipping and better
recovery, and more even tube wear. Its something worth something in
musicians amps which are
routinely used well into clipping the output stage.
>
> Any measurement with equal loads, such as observing the roll off, will
> show equal impedances. And it is trivial to derive mathematically as
> well since you have 'one' common current through the equal loads.
> Simply factor out the equal external loads leaving equal source
> impedances.
>
> >The theorists here who are making a mountain out of a molehill
> >could draw up the triode and a voltage gene + Ra resistor as a model in
>
> You seem to be confusing 'real circuit' with models. In a Thevenin
> model there is a ideal voltage source (ideal current source in the
> equivalent Norton) and an output impedance. There is no "triode
> and..."
The triode model I use is a perfect voltage generator with 3 terminals,
plus a resistance added to be equal to Ra taken to a 4th terminal
being the anode of the model.
One terminal is the cathode, one is a grid, and infinite Rin, and the
other generator output is
NOT the anode, but just the generator output, which is low Rout = 0.0
ohms and the signal output = µ x Vg-k.
From gene output to the anode there is a resistance = Ra.
This model can be used to easily work out whatever signal voltages will
exist at a, k and g for any vacuum tube.
Go to
http://turneraudio.com.au/tube-operation1.html
Take a look at Fig 2 nearly 1/2 way down the page.
I hope I have covered the subject at my website to promote understanding
of the use of modelling to some advanantage to those used to working
things out in a very basic
manner based on current flow and voltage appearances and the use of
Ohm's Law.
>
> >a CPI with equal anode and cathode loads
> >and prove to themselves how it all works by working out the voltages and
> >currents and then moving on to
> >derive the formulas for Rout at the anode, and Rout at the cathode, in
> >terms of µ, Ra, and RL.
>
> That's more akin to what you're doing, except you then ignore that the
> supposed 'source impedances' calculated have no apparent utility.or
> meaning for an equally loaded concertina.
Separate Rout measurements of Rout at a of k without making oads stay
equal does have limited utility; it tells us exactly what is there.
Meaning for use as a CPI comes when we add a condition of ensuring equal
loads always exist,
and changing anode and cathode loads equally when measuring Rout.
>
> I'd be interested if you can reveal some use for the 'unequal
> impedance' calculation because, off hand, I can't think of a single
> thing. Doesn't even tell me what happens with unequal loads because it
> wasn't calculated with those either.
There is no application I can think of where the fact of unequal Routs
is exploited for a benefit.
Of course RDH4 has a sample CPI where a normal CPI with one triode feeds
a
pair of following CPIs triodes, and in the following pair the
anode and cathode of one CPI are cross coupled with C to the other CPI
cathode and anode,
and the individually tested Routs at a and k become equal.
Its like a kind of CPI overkill to me, and ther's not one amp in which I
have ever seen such a thing.
Maybe it had its uses in scientific circuits of some sort.
>
> >> At this point it appears that the only way to make forward progress
> >> would be to agree on a method for measuring source impedance.
> >
> >I hope I have described a reasonable way to do it.
>
> It's reasonable. It just doesn't measure the Thevenin equivalent for a
> concertina with equal loads.
>
> >Measurers will find Rout at cathode a lot less then Rout at anode.
>
> Measurers who use equal loads will find equal Thevenin impedances.
>
> Measurers who break the concertina with unequal, or no, loads will
> find something else.
>
> >Sorry, but its true.
>
> Not when one defines output impedance as a Thevenin equivalent output
> impedance.
Well, OK, equivalant whatever, Rout is Rout at the end of the day.
>
> >However, just because the two source resistances are different, it don't
> >stop the CPI from being a
> >decent sort of phase inverter, and able to give good enough balance for
> >most amplifiers
> >as long as it isn't driven into overload.
>
> That's because, as long as the loads are equal it has equal Thevenin
> source resistances and since the Cs are equal the RC roll off is
> equal.
In fact the stray C and Miller C around the circuit can be asymetrical,
and
I have found the anode output sags at lower F than the cathode output.
hence the use of some compensating C across the Rk.
This boosts the anode output as F rises, and HF poles then become the
same at a and k.
>
> Which resolves the century old befuddlement of why the damn thing
> works despite those confounding 'different impedances' that had even,
> so called, 'experts' shoving 'build out resistors' on the thing to
> solve a problem with those confounding 'different impedances' that
> didn't exist.
>
> You simply accept that it works, despite the 'different impedances'. I
> have shown *why* it works and done so three ways: with the 'one
> current through equal loads' derivation and two models, one with your
> preferred unequal 'output impedances' (measured with a broken
> concertina) and one with the equal Thevenin equivalent output
> impedances.
I might have said more stuff than "it just works."
>
> They all work but the purpose behind concepts like 'output impedance'
> (the term being derived from Thevenin) is to simplify things and I
> submit that the 'unequal impedance' model has caused infinitely more
> confusion and problems that it ever resolved, so what is the purpose
> of it?
We need to know the unequal Routs are there if the loads become unequal.
But as Vchange / Ichange remain equal if both anode and cathode loads
are kept equal, at AF the CPI make a fine phase inverter.
It also buffers the input triode and balanced amp stage, so for a given
set of tubes the BW is very good.
But its 4 stages for an amp instead of a minimum of two, as in say
Quad-II.
4 triodes intead of two pentodes. We all know how the bean counters
voted.
They voted Williamson out into the Wilderness.
Patrick Turner.
John Byrns
flipper <fli...@fish.net> wrote:
> On Tue, 12 Aug 2008 16:22:18 GMT, Patrick Turner
> <in...@turneraudio.com.au> wrote:
>
> >
> >> However the most satisfying solution would be to abandon the model
> >> entirely, along with the questions it raises, and simply build the
> >> physical circuit and measure the resulting source impedances.
> >> Unfortunately it appears that would just take us back to square one,
> >> again raising the crucial question of how to properly measure the source
> >> impedances.
> >
> >
> >Just building something, observing it, measuring it and deciding what is
> >there
> >is trifle to complex and real for some around here. They hafta get orf
> >their bums, and go
> >into their workshop, and spend time actually doing something.
>
> You get yourself into trouble with those incessant knee jerk snide
> remarks of yours because this matter came up as a result of my doing
> exactly that. I BUILT the damn thing and measured it.
OK, great, that is exactly what I suggested a couple of days ago, you
should have said you had already done it. Of course building the
concertina is a relatively trivial task, the tricky bit is measuring the
concertina's two source impedances.
It would be helpful, and a positive contribution if you could explain
how you measured the source impedances, as well as how you determined
that they were equal?
So far all we have is people stating that they have measured the
concertina's two output voltages, found them to be equal, and then
forcefully asserting that "obviously if the concertina's two output
voltages are equal, then the two source impedances must also be equal"!
That assertion doesn't prove that the source impedances are necessarily
equal, as can be easily demonstrated by simply providing a counter
example that produces equal output voltages from unequal source
impedances. The bottom line is that a little bit of logic, something
sadly lacking in parts of this thread, tells us that the presence of
equal output voltages says absolutely nothing, one way or the other,
about the source impedances. To prove equal source impedances we need
something more than equal output voltages.
Moving on, later today I will post a response to your previous message
containing the answers to all the questions you say I have failed to
answer. I hope once you have those answers in hand, that you will
reciprocate by answering my question above.
John Byrns
flipper <fli...@fish.net> wrote:
> On Tue, 12 Aug 2008 09:31:41 -0500, John Byrns <byr...@sbcglobal.net>
> wrote:
>
>
> > I will simply be
> > looking for the "source" impedance.
>
> Define it.
The source impedance of an output is the impedance you see, or measure,
looking back into the output.
> Since you doggedly insist there can be one and only one model you most
> certainly are 'wedded' to 'it', despite refusing to define what 'it'
> is.
I did not say there could be "one and only one model", you are putting
words into my mouth again. What I said was that as far as I know, Henry
and I are using the same model, at least we were the last time Henry and
I went around on this subject several years back. I assume that if
Henry has switched models since then, he would speak up and loudly
proclaim the fact. If Henry has changed models I doubt I would have any
problem adapting his new model myself, thereby bringing us back into
congruence.
Did I refuse to define the model? Having not yet defined it in this new
thread is not the same thing as refusing to define it.
Here's the definition. The model of the concertina and its separate
loads consists of six elements. The concertina model proper consists of
a perfect voltage amplifier source and a series resistance representing
the small signal, frequency independent, anode resistance and u of the
concertina's triode, these two components are effectively an internal
Thevenin equivalent generator. In addition to the Thevenin equivalent
generator, two equal value resistors are connected from the Thevenin
equivalent generator's two output terminals to the AC or signal ground.
These two resistors represent the anode and cathode resistors used in
the concertina circuit to provide a path for the DC operating current
required by the triode. A Norton equivalent generator can replace the
Thevenin equivalent generator if desired, the two forms being equivalent.
That accounts for four of the elements in the complete system. The
final two elements in the complete system are two load impedances, Za
and Zk, one connected from the concertina's anode to ground and the
second connected from the concertina's cathode to ground. For the
purposes of this discussion of the balanced concertina Za and Zk are
made equal.
That's all there is to it. Note that this is a small signal model only
and does not take into account frequency dependent effects due to the
triode, such as the grid related capacitances, it does take into account
frequency dependent effects due to the loads Za and Zk.
Finally IIRC you asked me in another post how I measure impedance. I
have used three methods, the first two I have used on physical circuits
in my workshop, and a third theoretical method that I have used only on
mathematical models.
The first impedance measuring method that I use in my workshop is a GR
impedance bridge that I connect across the terminals of the device whose
impedance I wish to measure.
The second method I have used in my workshop is what I will call the
"Turner method" which Patrick described in a recent post to this group.
This method consists of feeding a sine wave signal into the input of the
DUT and measuring the output voltage. A resistor is then connected
across the output, while maintaining the same input voltage, and the
output voltage is again measured, with the added resistor connected.
The source resistance can then be calculated from the two voltages and
the value of the added resistance. Note however that this method only
works when the source impedance is purely resistive, it does not give
the correct answer when the source impedance is a complex impedance as
in the case of the concertina circuit with load.
The third method is what I call the "Pasternack" method after Henry
Pasternack who proposed it several years ago. I have not tried this
method in my workshop, as it would require building some test equipment
I don't have as well as a special test jig to make use of it. I have
however applied this method to mathematical models of various circuits.
This method requires two pieces of virtual or real test equipment. The
first is an AC current generator, and the second is a high impedance AC
voltmeter which can measure the magnitude of a voltage, as well as the
phase angle of the voltage relative to the phase of a reference signal.
In this case the reference signal is the phase of the current generator
output.
HP uses these instruments to measure the source impedances of the
concertina's two outputs by connecting the current generator between the
anode and cathode terminals of the concertina circuit, with the loads
disconnected. HP then uses the high impedance voltmeter to measure the
voltages that appear between the cathode and ground terminals, and
between the anode and ground terminals. From these voltage
measurements, as well as the value of the current produced by the
current generator HP then calculates the anode and cathode source
impedances.
I use the same two pieces of test equipment, however I connect them in
parallel between the two terminals I am measuring the impedance of. I
leave the anode load in place when measuring the cathode source
impedance, removing only the cathode load, and vice versa when measuring
anode source impedance. From the two voltage measurements, magnitude
and phase, and the current generator current setting I can then
calculate the source impedances for the two output terminals. These
source impedances are complex impedances, i.e. they have a reactive
component even for the simple resistive triode model. The complex
source impedance results from the load impedance Z that remains
connected to the output terminal not being measured.
Once I have the two source impedances, I next measure the voltages of
the two Thevenin equivalent voltage generators for the anode and cathode
terminals. I do this by disconnecting the current source from its
parallel connection across the voltmeter, instead feeding a known
voltage into the grid circuit, and then measuring the voltages developed
at the anode and cathode terminals of the concertina, using the same
load protocol as with the source impedance measurements. From these
measurements the Thevenin voltage generator function can be
characterized.
All these measurements must be repeated across the audio band to
completely characterize the source impedances and equivalent voltage
generator characteristics. The resulting source impedances and Thevenin
voltage generator functions can then be used to calculate the
gain/frequency characteristics the unbalanced concertina, as well as the
balanced concertina.
I think that about covers it, if I forgot something you have but to ask
and I will answer if I can.
Henry Pasternack
> It would be helpful, and a positive contribution if you could explain
> how you measured the source impedances, as well as how you
>determined that they were equal?
IMHO there is a rational and straightforward way to explain this
subject that makes it clear what the equal-impedance model means
and why it's a valid point of view. My compaint against you, Byrns,
is not that you take the position that the impedances are different.
It's clear what you mean and how you get to that point of view.
What does bother me, throughout all these years, is that you are
either unwilling or unable to make the effort to understand the other
point of view, and on that basis characterize me (and now Flipper)
as wrong/slippery/ foolish. I would go so far as to say you have
actively tried to avoid understanding my position because it is
incompatible with your larger belief systems to admit that I may
have a valid point. I say that just so we're clear what the argument
is about.
Anyway, I claim there are two aspects to the definition of output
resistance. The first apsect, an operational definition, says output
resistance is the real part of dv/di, where di is a small current flowing
in the output port. The second aspect, an abstraction, models the
device under test as a voltage source in series with an impedance,
where the output resistance is the real part of that impedance. I
think the first aspect is true by definition, and the second is true by
convention. In any event, I assert this is a reasonable and practical
definition.
The two models in question have the same architecture. It is a three-
port network with one input port and two output ports. The input
port is open-circuited. There are two voltage-controlled voltage
sources in the box, and two series resistors, each connected to one
of the output ports in the expected way. The voltage sources are
characterized by the equation Vout = k * Vin.
The models differ in the values of the components. In my model, R
and k are constant and Vin equals the input terminal voltage. Also,
the two halves are identical, i.e., R1 = R2 and k1=k2. In your model,
R, k, and possibly Vin are variable and depend on the external
components connected to the output ports. One of the features of
my model is that the three-port network can be split into two identical
two-ports with their inputs in parallel; this cannot be done for your
model, since it's not symmetrical and there are cross-dependencies
between the halves. Your model is more general than mine. If you
impose the equal load constraint, your model simplifies and then your
model and mine are identical.
With respect to measurements, we can use a sinewave generator
and an identical pair of test sets each containing an AC voltmeter.
Each voltmeter has a known input resistance. Inside the test set,
a resistor of known value may be connected in parallel with the
voltmeter using a switch. To perform an impedance measurement,
a signal of fixed amplitude is applied to the input port of the device
under test. A test set is connected to an output port and the voltages
are noted with the parallel resistor switched in and out. From these
readings it is possible to calculate the value of the series resistors in
the model of the device under test.
There are two test procedures. The Byrns procedure is:
a) Connect a test set to the plate output port and perform the two
measurements to determined the output resistance.
b) Disconnect the test set from the plate output port and repeat
the measurements with the test set connected to the cathode
output port.
My test procedure is:
a) Connect one test set to the plate output port and one test set to
the cathode output port.
b) Measure the voltages at both ports with the parallel resistors in
both test sets switched out of the circuit.
c) Measure the voltages at both ports with the parallel resistors in
both test sets switched into the circuit.
The result will be: In the Byrns test procedure, the measured output
resistances will differ. In my test procedure, the output resistances
will be equal and significantly lower than either of the two values
obtained in the Bryns test.
Now for interpretation. To the extent that both models and their
corresponding test procedures are documented and understood,
there can be no argument as to their validity. We can only argue
about the relevance and usefulness of the models, and the extent
to which their underlying assumptions match generally accepted
practices and principles.
I believe my model is a good model because it matches the typical
application (equal loads) of the split-load inverter, and it quickly
and economically predicts the HF rolloff behavior of the circuit
(ignoring strays). The notion of constant 'R' and 'k' is intuitive and
consistent with typical use of the Thevenin model. There is nothing
inherently wrong with using two test sets and making the measure-
ments simultaneously.
The Byrns model is more general and has the advantage that it
can handle any combination of unequal loads. The disadvantage
is that the resistances and the voltage source 'k' values are not
constant, but depend on the values of the load impedances. This
variability and interdependence, IMHO, is counter-intuitive to the
notion of a "real" output impedance and to common assumptions
about the the Thevenin/Norton model of output resistance.
This is a subjective call, but I would say the purpose of a model is
to impose a layer of abstraction that simplifies the representation of
a system at that level. I think John's model is of limited value because
it's basically just as complicated as the small-signal circuit model it
replaces. In that sense, our two models are not really comparable
because they represent two different levels of abstraction.
There is some sort of logical contradiction here, else there wouldn't
be this historical "paradox" about this circuit. As an aside, I would
observe again that a perfectly good way to measure output resistance
is to hang a cap across the output and measure the -3dB point. If
you do this to a real split-load inverter with two caps (as is proper
for a balanced circuit), you apparently get equal output resistances.
I agree with Flipper that this is an obvious and quite legitimate test
and interpretation of the results. The difficulty some people have in
accepting it seems to lie mostly in their ingrained notions of what
cathode follower and common cathode amplifier are and how they
"must" behave.
I think the single most important statement Flipper has made in this
discussion is when he pointed out that Byrns is not measuring the
split-load inverter, but is separately measuring a cathode follower
and an unbypassed common-cathode amplifier. To the extent that
'R' and 'k' one one port depend on the load at the other port in
Byrns's model, he is measuring two different circuits with his test,
since connecting the meter to one port or the other changes what's
inside his black box model of the DUT.
I anticipate several of John's objections, but my feeling here is that
I don't have to defend my model as the only viable model (it isn't),
but only to show it's reasonable (it is), contrary to Byrn's tiresome
historical remarks. And that's all I have to say.
I am sure John will have many unsatisfying things to say in reply.
But now I have to get back to work.
-Henry
John Byrns
"Henry Pasternack" <f...@bar.com> wrote:
> I am sure John will have many unsatisfying things to say in reply.
> But now I have to get back to work.
Hi Henry,
I was getting really irritated with łFlipper˛ and his mantra of łthere
are two different models˛ when he seemingly wouldn't attempt to łdefine˛
the two models. His constant reference to Thevenin and Norton Models as
if they explained what he meant by two different models furthered my
confusion. After reading your post I finally realized what he was
probably talking about. All became clear when I realized that I was
being confused because there aren't two different models, there are
actually three different models involved. The first model being the one
I was talking about that mathematically describes the component topology
and values used in the actual concertina circuit implementation. The
second and third models are the two models based on your measurements
and on my measurements. Hopefully I now correctly understand what he
meant, although it doesn't really say much to resolve our disagreement
about whether or not the two source impedances are equal or not.
I was also annoyed when I kept asking łFlipper˛ what his basis was for
sayingthat the anode and cathode source impedances were equal and he
would come back with statements something like łthe loads and the
voltages are equal so the source impedances appear to be equal˛. I have
not looked up one of his exact quotes, but I think they were something
to that effect. I really don't know what he may have been trying to
say, I originally interpreted it as his version of a proof, but after
thinking about it today, it occurred to me that he may have meant the
statement not as a proof, but as a sort of political compromise.
Whether he meant it that way or not, I love it in that new sense, it has
just the right number of weasel words to neatly encompass both your view
and mine without being too definite about what the relation of the two
impedances might be to each other.
There is also a third test procedure in addition to the two you
described. Call this procedure the łNew Byrns˛ procedure. I would
appreciate your comments on this new procedure.
Note that under the balance assumption, where the two loads and the
voltages across them are equal, no current will flow from the junction
of the two loads to ground. This allows us to disconnect the two loads
from ground while keeping the ends of the two loads connected to each
other.
The third test procedure, the łNew Byrns˛ procedure then becomes:
a) Remove the two balanced loads and replace then with a single load of
twice the impedance of either of the original two loads, using the
observation above.
b) Connect a single test set between the anode and cathode terminals of
the concertina, and perform the measurements to determine the output
resistance.
This output resistance should be twice the value of the output
resistance measured with your two test set procedure and can be used in
the same way to easily calculate the 3 dB frequency without raising the
prickly issue of whether or not the anode and cathode source impedances
are equal or not.
A question for you, with respect to your test procedure you state that
łIn my test procedure, the output resistances will be equal and
significantly lower than either of the two values obtained in the Bryns
test.˛ You have stated this before, are you sure that your output
resistance is significantly lower than either of the two values obtained
in the original Byrns test? That doesn't seem to meet the common sense
test for reasonableness; however stranger things have proven true, so I
will have to put it on my list of things that need verifying one way or
the other.
Patrick Turner
flipper wrote:
>
> On Wed, 13 Aug 2008 10:50:58 GMT, Patrick Turner
> <in...@turneraudio.com.au> wrote:
>
> >
> >
> >flipper wrote:
> >>
> >> On Tue, 12 Aug 2008 16:22:18 GMT, Patrick Turner
> >> <in...@turneraudio.com.au> wrote:
> >>
> >> >
> >> >> However the most satisfying solution would be to abandon the model
> >> >> entirely, along with the questions it raises, and simply build the
> >> >> physical circuit and measure the resulting source impedances.
> >> >> Unfortunately it appears that would just take us back to square one,
> >> >> again raising the crucial question of how to properly measure the source
> >> >> impedances.
> >> >
> >> >
> >> >Just building something, observing it, measuring it and deciding what is
> >> >there
> >> >is trifle to complex and real for some around here. They hafta get orf
> >> >their bums, and go
> >> >into their workshop, and spend time actually doing something.
> >>
> >> You get yourself into trouble with those incessant knee jerk snide
> >> remarks of yours because this matter came up as a result of my doing
> >> exactly that. I BUILT the damn thing and measured it.
> >>
> >> So, with all due respect to you and your bums, sit on it.
> >
> >OK, Point taken, but some here are arm chair wanabes.
>
> That may be but they're not in the discussion. But, at any rate, I
> accept the 'ok'.
>
> >> >But ya don't need to all that. Blind Freddy can see that if you measure
> >> >the Rout
> >> >at the anode by adjusting the anode load and only the anode load, the
> >> >Rout
> >> >= Vchange / Ichange, which is how you measure the Rout of anything.
> >>
> >> Not when equal loads is inherent to the circuit and a required
> >> condition.
> >
> >But when one talks about the Rout at one point in a circuit,
> >what is usually meant is that its taken as is at that point,
> >and without any load adjustments elsewhere.
>
> I am aware of that but that is precisely the 'problem'. It just
> doesn't work with a concertina and if you do it that way you get
> essentially useless results.
Well, if you use the classic way to measure the Rout of anything by
changing the load
and recording the Vchange, and I change, Ro can be found, but sure,
because the Rout
at a and k are very different if the measurement is done by applying
only one same load change
to each a and k output, then the answer for Ro is useless.
As I said, you could make the same load change to each of a and k, and
you should measure
equal Vchange and I change, and Ro at a and k will simply be Vchange /
Ichange and the same for a or k.
>
> >The Vchange / I change can be used to measure Rout easily for any amp
> >output.
> >
> >In the case of the CPI, it can be done if you specifiy that the load
> >change
> >to anode and cathode will be equal.
> >Then the because the same current flows through cathode load, tube, and
> >anode load,
> >the Ichange is equal, and because the TWO loads are kept equal, V change
> >will also be equal,
> >so you'd think Rout is the same from both terminals.
> >
> >It is, but subject to conditions.
>
> Bingo... as you said, it *is* (the same).
>
> So why were you chastising folks for saying exactly what you just
> said?
Because of the condition of the test for Rout that needs to be
specified.
Conditions apply for the truth to be true.
>
> >Unconditionally, its not.
>
> I am aware it's subject to conditions and the conditions have ALWAYS
> been stated, from the very first post to the last.
>
> It also happens to be the overwhelmingly common case and folks often
> go to great lengths to keep it equal and 'balanced'. Unfortunately, in
> the burning quest to do so, the befuddlement of an unequal output
> impedance model has screwed up more than a few.
>
> >> Unequally loaded it isn't a 'concertina' and it doesn't behave like a
> >> 'concertina'. In fact, measuring your way you'd rip the thing up and
> >> throw it out because the outputs would be nothing akin to equal and,
> >> so, of no use as a 'phase inverter'.
> >
> >Unless you has a pot to lower the higher VO to be equal to the lower VO.
> >
> >But it wastes gain, so nobody does it.
>
> The only reason I can imagine anyone even thinking of such a
> contraption is if they were befuddled by the unequal impedance model
> and were trying to 'fix' the problem that doesn't exist.
"Whatever" as they say....
>
> >> >If you repeat the same load adjustment to the cathode load and leave the
> >> >anode load alone,
> >> >you will find Rout is less then at the anode.
> >>
> >> You're not measuring a concertina.
> >
> >A concertina is merely a normal single ended common cathode triode amp
> >stage, but one with
> >a cathode resistor equal to the anode resistor.
> >
> >So when measuring a concertina, you are measuring a common cathode
> >amplifier stage.
>
> Nope. Because you left out that the concertina has two, not one,
> outputs with equal loads, and that is not a trivial condition. As
> evidenced by the near 'magical' result of the seemingly disparate
> output impedances of the common cathode amp becoming equal. Except, of
> course, you don't have two 'output' impedances in the common cathode
> amp, there's only one, so there's not really a comparison.
Nothing stopping you from using the cathode as an output from a common
cathode amp
**of any kind** including where you have RLa = RLk.
>
> They just aren't the same thing, which is why measuring it as one
> thing doesn't give you the same answer as measuring it when it's the
> other.
The concertina to my mind is merely a common cathode stage with a lot of
local current FB from
its unbypassed Rk.
OK, so you take outputs from both a and k.
It doesn't stop the concertina being a common cathode amp.
>
> >> >And you'll find the cathode is a voltage source, ie, Rout < RL at the
> >> >cathode,
> >> >and Rout at the anode is a current source, ie, Rout > RL at the anode.
> >>
> >> You're not measuring a concertina.
> >>
> >> >Now this is true of any common cathode amplifier with an unbypassed Rk,
> >> >and you test the Rout at
> >> >anode and cathode separately.
> >>
> >> That's right, a common cathode amplifier, not a concertina.
> >
> >As I said, a concertina *is* a common cathode amp......
>
> No it is *not*. It looks a hell of a lot like one but a common cathode
> amplifier has ONE output and a concertina has TWO, with equal loads.
So what about the number of outputs?
Its still a basic common cathode amp.
Another way to get phase inversion is to simply use a common cathode amp
with
a gain of exactly -1.0, ie, a triode common cathode amp is set up with
an unbypassed Rk
which is slightly lower in value than the RLa, and Vg = -Va.
So you have the input signal from somewhere external, maybe a CD player,
and you create an opposite
phase signal of exactly the same amplitude, and the two phases can then
be applied to a fully
balanced PP power amp with balanced series voltage GNFB. ARC did this
maybe 30 years ago.
The word "Concertina" does not make it illegal to say the concertina is
a common cathode amp.
It is a common cathode amp, but one with special features, implied by
the word concertina.
The "squeeze box" instrument stays put, but the player works the 2
handles in opposite directions.
>
> >The word concertina is used so everyone knows the cathode load = anode
> >load,
> >hence Va = Vk.
>
> That's hunky dory.
>
> >> >It would be possible to rig up the CPI so that Rout is the same at a and
> >> >k,
> >> >but it'd need you to reduce anode RL and increase the cathode RL until
> >> >the Rout was the same at a and k.
> >> >But then the voltages wouldn't be equal at all, so its not a useful
> >> >exercize.
> >>
> >> Nope, because if one defines 'output impedance' per the Thevenin model
> >> then a concertina already has equal Thevenin 'output impedances' as
> >> long as the loads are equal.
> >
> >If measured separately, you get what ya get, if measured conditioanlly,
> >you get something else,
>
> Exactly.
>
> > a convenient measure.
>
> Well, one convenience is it measures the thing as it actually is and
> used. Another is it produces a useful result, which is THE point to
> doing a calculation in the first place.
>
> >I have never worked out exactly what the conditional Rout of the
> >CPI actually is. But its somewhere higher than a cathode folower, and
> >lower than from
> >a normal common cathode amp at its anode and with fully bypassed
> >cathode.
>
> Henry came up with a number lower than a cathode follower and I think
> Preisman did as well.
I don't see how it could be lower, but I have never needed to work it
out.
You can have 22k for RLa and RLk for a 6SN7, and have Va = Vk = 2V,
and then change the cap coupled loads from say 150k to 22k, and the Vk
and Va will stay equal,
but the drop in voltage is low, like a CF.
If the following cap coupled loads become too low compared to the dc
carrying RLs,
then the undistorted voltage range is reduced, and you get sudden cut
off distortions.....
>
> >
> >Math experts should have come up with all the releveant figures by now,
> >but I've never
> >*needed* to calculate the Rout, so I have never have.
>
> That's ok. It doesn't mean someone else doesn't care, though.
Hmm, we have not seen too much care around here and have not seen
anyone say what the Rout actually is for CPI if a&k loads are always the
same.
>
> Just knowing they're equal, never mind the 'value', would have saved a
> hell of a lot of confusion over the last century, though.
>
> >> >The only way to ensure the CPI has equal Rout at a and k would be to
> >> >direct couple
> >> >a pair of cathode followers to cathode and anode, and then you'd find
> >> >the two Routs would be the same
> >> >and each would be equal to what you'd get with any CF.
> >>
> >> There is no need because if one defines 'output impedance' per the
> >> Thevenin model then a concertina already has equal Thevenin 'output
> >> impedances' as long as the loads are equal.
> >
> >"as long as the loads are equal" is the condition needed for equal Rout
> >at each terminal.
> >
> >What if they were not in a dynamic working amp?
>
> Doesn't matter as long as the load impedances are equal,
Well there is a point where the loads suddenly do become unequal, at
grid current
in a following stage.
As one phase goes +, it hits and stalls with Ig, but the other phase
going -
has no grid current.
Guess which output tends to charge up the coupling caps the most.
>
> >
> >This becomes a fact when a CPI runs into grid current powering output
> >tubes.
> >The grid current affects the anode signal supply far more than the
> >cathode supply,
> >and the amp clipping becomes grossly asymetrical, ie, like a dogs'
> >breakfast,
> >with gross asymetrical dc offsets.
>
> None of the 'impedance' models are valid when it exits linear
> operation and that's a stated condition for a Thevenin output
> impedance.
>
> > So in guitar amps, 99% use a
> >balanced amp or LTP to drive the output stage which gives symetrical
> >clipping and better
> >recovery, and more even tube wear. Its something worth something in
> >musicians amps which are
> >routinely used well into clipping the output stage.
>
> Yes, I know. I've built them. But it's not germane to a discussion of
> concertina output impedance.
> That's fine if one wants to model a triode, and there are good reasons
> why one might, but in a classic Thevenin model of output impedance
> there is no 'triode' (nor a model of one), or anything else but a
> voltage source and a single output impedance. That's it's purpose and
> the 'definition' of "output impedance."
>
> >> >a CPI with equal anode and cathode loads
> >> >and prove to themselves how it all works by working out the voltages and
> >> >currents and then moving on to
> >> >derive the formulas for Rout at the anode, and Rout at the cathode, in
> >> >terms of µ, Ra, and RL.
> >>
> >> That's more akin to what you're doing, except you then ignore that the
> >> supposed 'source impedances' calculated have no apparent utility.or
> >> meaning for an equally loaded concertina.
> >
> >
> >Separate Rout measurements of Rout at a of k without making oads stay
> >equal does have limited utility; it tells us exactly what is there.
>
> Maybe, if you define "what.". But 'what' is not "output impedance"
> when you have two loaded outputs.
>
> >Meaning for use as a CPI comes when we add a condition of ensuring equal
> >loads always exist,
> >and changing anode and cathode loads equally when measuring Rout.
>
> That's a different derivation and measurement.
>
> >> I'd be interested if you can reveal some use for the 'unequal
> >> impedance' calculation because, off hand, I can't think of a single
> >> thing. Doesn't even tell me what happens with unequal loads because it
> >> wasn't calculated with those either.
> >
> >There is no application I can think of where the fact of unequal Routs
> >is exploited for a benefit.
>
> Makes me wonder why you're so enthusiastic about a useless
> calculation.
>
> >Of course RDH4 has a sample CPI where a normal CPI with one triode feeds
> >a
> >pair of following CPIs triodes, and in the following pair the
> >anode and cathode of one CPI are cross coupled with C to the other CPI
> >cathode and anode,
> >and the individually tested Routs at a and k become equal.
> >
> >Its like a kind of CPI overkill to me, and ther's not one amp in which I
> >have ever seen such a thing.
> >
> >Maybe it had its uses in scientific circuits of some sort.
>
> I'm not interesting in calculating the output impedance of that.
Too useless for you?
Probably RDH4 has the expressions in math for all the Routs you can ever
think of.
I just don't know them all.
>
> >> >> At this point it appears that the only way to make forward progress
> >> >> would be to agree on a method for measuring source impedance.
> >> >
> >> >I hope I have described a reasonable way to do it.
> >>
> >> It's reasonable. It just doesn't measure the Thevenin equivalent for a
> >> concertina with equal loads.
> >>
> >> >Measurers will find Rout at cathode a lot less then Rout at anode.
> >>
> >> Measurers who use equal loads will find equal Thevenin impedances.
> >>
> >> Measurers who break the concertina with unequal, or no, loads will
> >> find something else.
> >>
> >> >Sorry, but its true.
> >>
> >> Not when one defines output impedance as a Thevenin equivalent output
> >> impedance.
> >
> >Well, OK, equivalant whatever, Rout is Rout at the end of the day.
>
> That's the problem, it isn't and you get completely different results
> when you 'measure' under different conditions. 'Single sided' you get
> one thing, equal loads gives you equal impedances, and unequal loads
> gives you a whole range of impedances. 'Rout' is anything but 'Rout'.
>
> >> >However, just because the two source resistances are different, it don't
> >> >stop the CPI from being a
> >> >decent sort of phase inverter, and able to give good enough balance for
> >> >most amplifiers
> >> >as long as it isn't driven into overload.
> >>
> >> That's because, as long as the loads are equal it has equal Thevenin
> >> source resistances and since the Cs are equal the RC roll off is
> >> equal.
> >
> >In fact the stray C and Miller C around the circuit can be asymetrical,
> >and
> >I have found the anode output sags at lower F than the cathode output.
> >hence the use of some compensating C across the Rk.
> >This boosts the anode output as F rises, and HF poles then become the
> >same at a and k.
>
> Come on Pat, you're grasping at any and everything. Everyone,
> regardless of the model, has specifically said local parasitics are
> being ignored and we're limiting operation under them.
If you want an ideal square wave at 5kHz in a Williamson,
you would find you'll get the best looking one where you have taken the
trouble to
add a small C across Rk of the CPI.
Lots of ppl do it. I just re-wired a VAC amp, there is the C, and 47pF
across 22k.
Its there to improve the HF performance.
> >> Which resolves the century old befuddlement of why the damn thing
> >> works despite those confounding 'different impedances' that had even,
> >> so called, 'experts' shoving 'build out resistors' on the thing to
> >> solve a problem with those confounding 'different impedances' that
> >> didn't exist.
> >>
> >> You simply accept that it works, despite the 'different impedances'. I
> >> have shown *why* it works and done so three ways: with the 'one
> >> current through equal loads' derivation and two models, one with your
> >> preferred unequal 'output impedances' (measured with a broken
> >> concertina) and one with the equal Thevenin equivalent output
> >> impedances.
> >
> >I might have said more stuff than "it just works."
>
> Well, you usually say 'more stuff'. Whether it's related to the topic
> is another question and it's true I haven't heard everything you've
> ever said.
>
> But this last time around you didn't say anything about how in the
> world different impedances into equal capacitive loads could possibly
> come out with an equal roll off. All you said was the unequal
> impedances don't stop it from working just fine.
>
> Well, as you said above, the reason is the output impedances *are*
> equal, not different.
Well, I suggest you examine a working amp more closely.
You might find the reason why some makers add a C across Rk of a CPI.
Its to slightly boost the anode output which sags before the cathode
output.
Most makers don't bother, like they don't bother to do a whole range of
stuff
because they work down to a price, not up a standard of quality.
>
> >> They all work but the purpose behind concepts like 'output impedance'
> >> (the term being derived from Thevenin) is to simplify things and I
> >> submit that the 'unequal impedance' model has caused infinitely more
> >> confusion and problems that it ever resolved, so what is the purpose
> >> of it?
> >
> >We need to know the unequal Routs are there if the loads become unequal.
>
> The Routs you calculate are useless for that as well because it
> doesn't take into account unequal loads any more than it does equal
> ones.
>
> That derivation only works for ONE output at a time..
>
> >But as Vchange / Ichange remain equal if both anode and cathode loads
> >are kept equal, at AF the CPI make a fine phase inverter.
>
> Right. And the result of a V/I calculation is generally called
> "impedance" so equal V/I means equal output impedances.
>
> >It also buffers the input triode and balanced amp stage, so for a given
> >set of tubes the BW is very good.
> >But its 4 stages for an amp instead of a minimum of two, as in say
> >Quad-II.
> >4 triodes intead of two pentodes. We all know how the bean counters
> >voted.
> >They voted Williamson out into the Wilderness.
>
> "Bean counters" don't get a vote. They count beans.
>
> See Pat, among other things I've *been* both a designer and a Product
> Manager so don't pretend to tell me how 'bean counters' voted or that
> they told me 'how many' of this or 'what' I could or could not put in
> a product.
Bean counters destroyed most quality in most products.
They are there to *remove quality*
If they'd made cars with stainless steel bodies back in the 1950s,
they'd still be around. But they made cars with thin ordinary sheet
steel that wasn't
meant to last longer than 5 years if you were very lucky.
It rusted away as you watched it in damp weather.
Bean counters created the most important commandment for business:-
Thou Shalt Not Make Anything to Last Long.
Some bastard upset the apple cart and invented a good way of painting
the
steel on the concealed inside areas of a car, so it lasted 15 years.
It was such a saving for the Ordinary Man, and his Struggling Missus,
that cars made which didn't rust got the sales.
Reluctantly, bean counters around the world were embarrassed into
recommending their companies extend the plant to include painting the
hidden surfaces of a car body.
They were all forced into it. They sure didn't like to have to pay more
for production.
They slugged the customer real hard for the improvement of course, more
than they should have,
because they'd point out how much longer something would last, and
instead of buying 3 cars in 15 years you'd only need one.
Boy they had it on easy street, because the marketeering arsols
brainwashed everyone
to feel sick and tired of an old model of anything, so they still
changed cars every 5 years.
Then the funders got in on the act and lent money to anyone for
anything,
and what did a price then mean? Just a repayment.
Many people are useless and making anything, so they end up
becoming an a artist, or an accountant, or doer of something
that is often useless, except to facilitate shit going out the factory
gate
so the company won't go broke.
One person in one company removes quality, or moves production to China,
and sacks all the US workers,
and saves the company having to spend so high in production costs, so
the company can lower its prices and become much more
competitive and profitable. Every other company has to follow after the
first or else they go broke.
Anyway, bean counters ridiculed that Williamson fella, what fuckwit they
all said, he'll ruin us all!!
I cannot name a single well known amplifer manufacturer who used
Williamson's OPT design
for a huge run of amps.
Fancy having to make such horribly complex OPTs that take so much
labour! Ridiculous they all howled.
But by 1960, Fancy having to use vacuum tubes!!, send 'em to the tip,
let's get those cool running transistors going.
Then anything that worked in the analog realm became BS, and suddenly,
its all digital everything.
Some aspects of progress are good, like me being able to type this very
very cheap telegram,
and not have to pay 10C a word, after spelling it out across a Post
Office desk to a girl.
So the bean counters have not ruined everything.
Make it cheap, light, smaller; let it run hotter, and harder, and let's
take out the good stuff so it goes up in smoke a week after the warranty
period expires.
And while we are at it, lets have a National trade Conferance to agree
on the same crummy standards,
so that the consumers don't have a choice. After smoke it won't matter
who they go to after changing brands,
its all basically the same shit.
And all the entrepreneurs and accontants and bean counters ansd arsoles
all agreed
and colluded with each other to minimize competition and reduce quality
to
the lowest possible denominator. Nice and cosy. SNAFU.
Its very difficult to avoid the ticky tacky and sameness about many
products of the same price
in this world.
With hi-fi, if you know enough, you can avoid all the junksters, and
spend time
in your workshop and emerge later with something much better than the
junksters ever
would let you have.
But you can't build a motor vehicle of your own design.
Naughty naughty, far too many regulations and licences needed. Ditto
your own aeroplane.
Or any plumbing on your house.
And because more folks would die as a result of such freedoms.
But amps rarely kill, so they are OK, like growing your own tomatoes.
I know who I like to throw rotten tomatoes at.
Patrick Turner.
Henry Pasternack
news:48A45DBA...@turneraudio.com.au...
>> Henry came up with a number lower than a cathode follower and I think
>> Preisman did as well.
>
> I don't see how it could be lower, but I have never needed to work it
> out.
And yet it is true. In fact, for an example I calculated, the equal-load
effective output impedance was an order of magnitude lower than the
cathode-only output impedance. Read about it here:
http://groups.google.com/group/rec.audio.tubes/msg/3f5394ad0426aeb1
Consider the case where you infer output resistance by measuring the
-3dB point when driving a capacitive load. With a single capacitor at
the cathode you will get one result. Now, adding an identical capacitor
at the plate will reduce the cathode output impedance because it bypasses
the plate resistance.
-Henry
Andre Jute
> . Now, adding an identical capacitor
> at the plate
Whyever?
John Byrns
"Henry Pasternack" <f...@bar.com> wrote:
> "Patrick Turner" <in...@turneraudio.com.au> wrote in message
> news:48A45DBA...@turneraudio.com.au...
> >> Henry came up with a number lower than a cathode follower and I think
> >> Preisman did as well.
> >
> > I don't see how it could be lower, but I have never needed to work it
> > out.
It isn't, you have to keep in mind that you are dealing with the
slippery fish, who in this case is misquoting Henry. Henry's original
claim was that his CPI source impedance was lower than the source
impedance at the cathode of the CPI when measured by the Byrns method,
and that is indeed true, the slippery fish has incorrectly equated the
³Byrns² method CPI cathode source impedance with the source impedance of
a cathode follower in his statement above. They are not the same thing,
the source impedance at the cathode of a CPI is higher than the source
impedance of a cathode follower. The reason for this is the extra
impedance in series with the anode of the CPI, which raises the cathode
source impedance. Hence it makes perfect sense for Henry's CPI source
impedance, which is half of the cathode to anode source impedance, to be
lower than the impedance measured at the cathode of the CPI using the
Byrns method, while still being greater than the source impedance of a
true cathode follower. Henry's response below is correct because he
failed to notice that Flipper had substituted the term ³cathode
follower² for the original ³CPI cathode-only² output. You can see how
this result comes about from the equations defining the operation of the
CPI that are presented in the message that Henry was responding to with
the message he links to below.
> And yet it is true. In fact, for an example I calculated, the equal-load
> effective output impedance was an order of magnitude lower than the
> cathode-only output impedance. Read about it here:
>
> http://groups.google.com/group/rec.audio.tubes/msg/3f5394ad0426aeb1
>
> Consider the case where you infer output resistance by measuring the
> -3dB point when driving a capacitive load. With a single capacitor at
> the cathode you will get one result. Now, adding an identical capacitor
> at the plate will reduce the cathode output impedance because it bypasses
> the plate resistance.
I'm not sure why you are getting into the capacitor business, what you
said is true even without the necessity for adding capacitors, at least
for the component values used in your example referenced above.
I would suggest that anyone interested in this subject read the entire
thread the above referenced message was taken from, it is the definitive
work on the subject. Ideally the thread should be read from point where
the subject changes to the concertina from the original feedback topic,
through to the end of the thread where Henry calls me an ³idiot². At a
minimum the message Henry is responding to, with the above referenced
message, should be carefully read, it can be found here.
http://groups.google.com/group/rec.audio.tubes/msg/5cfe562e8a81ded7
Contrary to the warning at the end, I think it turned out that the
equations contained no typos.
There is a lot of other interesting stuff in the thread. There is a
discussion of my anode and cathode transfer functions, and how they
degenerate into a form identical to Henry's when you make the anode and
cathode load impedances equal, as in a well balanced concertina.
Another interesting point is where I ³Aced² what I will call the
³Flipper² challenge. At one point Henry challenged me to use my
equations to tell him the -3 dB point for the example he presented in
the reference above, with 470 pF capacitors added to the anode and
cathode loads. This turned out to be a trivial exercise, as it turns
out my equations are no harder to use to determine the -3 dB point for
the balanced case than his equations are. I have so far only skimmed
over that part of the thread, so I don't remember exactly how I made the
-3 dB calculation at that time, which is not surprising given that I had
forgotten the entire thread until Henry pointed it out above. However
it occurs to me now that if we substitute separate R & C load values
into the transfer function equation in place of the complex ³Z² that I
used, we will get a transfer function equation that explicitly includes
the relevant RC time constant term that Flipper was looking for.
Flipper has given me a lot of guff about Thevenin and Norton; it is
interesting to read the old thread, where I referred to the source
impedances I had calculated as ³Thevenin equivalent source impedances².
Jack Crenshaw complained about my use of the ³T² word, saying I was
merely using it to impress people by ³name dropping², and that in this
group it would be more appropriate for me lose the ³T² word and simply
refer to the ³source impedance². To accommodate Jack I dropped the ³T²
word from my posts, however I soon had Henry on my case asking why I
didn't discuss the ³Thevenin source impedance² suggesting it was because
I didn't understand Thevenin. One can but wonder why Jack didn't take
Henry to task for name-dropping too?
That old thread it is a good read and contains much other material of
interest, I plan to carefully read the entire thread, having quickly
scanned parts of it last night. I have to say thank you to Henry for
pointing out this wonderful old thread.
Patrick Turner
flipper wrote:
>
> On Fri, 15 Aug 2008 13:01:41 -0500, John Byrns <byr...@sbcglobal.net>
> wrote:
>
> >In article <oJ6dnTiJCeQC5TnV...@rcn.net>,
> > "Henry Pasternack" <f...@bar.com> wrote:
> >
> >> "Patrick Turner" <in...@turneraudio.com.au> wrote in message
> >> news:48A45DBA...@turneraudio.com.au...
> >> >> Henry came up with a number lower than a cathode follower and I think
> >> >> Preisman did as well.
> >> >
> >> > I don't see how it could be lower, but I have never needed to work it
> >> > out.
> >
> >It isn't, you have to keep in mind that you are dealing with the
> >slippery fish, who in this case is misquoting Henry.
>
> I've tried to stay cordial but if hurling insults is your opinion of
> the 'good way' to make a case then let me know because, in the spirit
> of collegial accommodation, I'll gladly hurl a few grenades your way
> if it'll make you happy.
>
> > Henry's original
> >claim was that his CPI source impedance was lower than the source
> >impedance at the cathode of the CPI when measured by the Byrns method,
> >and that is indeed true, the slippery fish has incorrectly equated the
> >³Byrns² method CPI cathode source impedance with the source impedance of
> >a cathode follower in his statement above.
>
> I'm glad to see you finally agree with Henry.
>
> > They are not the same thing,
> >the source impedance at the cathode of a CPI is higher than the source
> >impedance of a cathode follower.
>
> And just who said a cathode follower can't have a resistor in the
> anode circuit?
Well, the guy who said the lowest Rout is only possible if there is no
resistor in the anode circuit of a CF.
When one selects to use a CF, one does so to get Rout as low as
possible.
No need to waste a resistor.
>
> Any rational person would presume I meant the circuit as it is because
> that's the circuit under discussion. And they'd be correct.
>
> Lord only knows how in the world you come up with the whole cloth
> fantasy I somehow meant a different circuit with the anode load
> removed.
>
> And if you wondered what I meant then why didn't you ask, instead of
> accusing me of intentional deceit?
>
> Or, if you thought I goofed then why didn't you 'help' me by
> explaining it, instead of accusing me of intentional deceit?
>
> What is it with you that everything gets interpreted as some kind of
> nefarious plot?
People are people around here, suspicious, devious even, wacky, even
interested in vacuum tubes of all things
to be interested in. Crazy. Just human nature.
>
> > The reason for this is the extra
> >impedance in series with the anode of the CPI, which raises the cathode
> >source impedance. Hence it makes perfect sense for Henry's CPI source
> >impedance, which is half of the cathode to anode source impedance, to be
> >lower than the impedance measured at the cathode of the CPI using the
> >Byrns method, while still being greater than the source impedance of a
> >true cathode follower.
>
> Oh, so now it's a 'true' cathode follower. As opposed to what? A
> 'false' cathode follower?
>
> > Henry's response below is correct because he
> >failed to notice that Flipper had substituted the term ³cathode
> >follower² for the original ³CPI cathode-only² output.
>
> Because Henry knows I mean the ³CPI cathode-only² output when I say
> cathode follower.
I thought that too, but maybe JB didn't, and who meant what gets a
little confusing afer awhile.
But I thought HP said that in ab CPI, aRout = kRout where loads are
always equal and
each Rout < CF Rout if the triode was used as a pure CF with no anode
load.
It can easily be checked by setting up a 6SN7 triode in a typical CPI
circuit, say 22k a and k RLdc loads,
then have 1uF coupling caps to place additional 22k equal cap coupled
RLs to both a and k
so that the output voltage can be measured with 44k total tube load, or
22k total tube load.
To convert to CF, the anode cap is taken to 0V, and the VO with 22k is
again noted,
and then with another 22k cap coupled to 0V.
Better to know by finding out rather than shooting the breeze endlessly
here.
>
> > You can see how
> >this result comes about from the equations defining the operation of the
> >CPI that are presented in the message that Henry was responding to with
> >the message he links to below.
> >
> >> And yet it is true. In fact, for an example I calculated, the equal-load
> >> effective output impedance was an order of magnitude lower than the
> >> cathode-only output impedance. Read about it here:
> >>
> >> http://groups.google.com/group/rec.audio.tubes/msg/3f5394ad0426aeb1
> >>
> >> Consider the case where you infer output resistance by measuring the
> >> -3dB point when driving a capacitive load. With a single capacitor at
> >> the cathode you will get one result. Now, adding an identical capacitor
> >> at the plate will reduce the cathode output impedance because it bypasses
> >> the plate resistance.
> >
> >I'm not sure why you are getting into the capacitor business,
>
> Because it's a valid means of measuring the circuit despite your
> confusion about it.
>
> > what you
> >said is true even without the necessity for adding capacitors, at least
> >for the component values used in your example referenced above.
> >
> >I would suggest that anyone interested in this subject read the entire
> >thread the above referenced message was taken from, it is the definitive
> >work on the subject. Ideally the thread should be read from point where
> >the subject changes to the concertina from the original feedback topic,
> >through to the end of the thread where Henry calls me an ³idiot². At a
> >minimum the message Henry is responding to, with the above referenced
> >message, should be carefully read, it can be found here.
> >
> >http://groups.google.com/group/rec.audio.tubes/msg/5cfe562e8a81ded7
> >
> >Contrary to the warning at the end, I think it turned out that the
> >equations contained no typos.
> >
> >There is a lot of other interesting stuff in the thread. There is a
> >discussion of my anode and cathode transfer functions, and how they
> >degenerate into a form identical to Henry's when you make the anode and
> >cathode load impedances equal, as in a well balanced concertina.
> >Another interesting point is where I ³Aced² what I will call the
> >³Flipper² challenge.
>
> Oh? And just what is the ³Flipper² challenge?
>
> > At one point Henry challenged me to use my
> >equations to tell him the -3 dB point for the example he presented in
> >the reference above, with 470 pF capacitors added to the anode and
> >cathode loads. This turned out to be a trivial exercise, as it turns
> >out my equations are no harder to use to determine the -3 dB point for
> >the balanced case than his equations are. I have so far only skimmed
> >over that part of the thread, so I don't remember exactly how I made the
> >-3 dB calculation at that time, which is not surprising given that I had
> >forgotten the entire thread until Henry pointed it out above. However
> >it occurs to me now that if we substitute separate R & C load values
> >into the transfer function equation in place of the complex ³Z² that I
> >used, we will get a transfer function equation that explicitly includes
> >the relevant RC time constant term that Flipper was looking for.
>
> No one has ever disputed that both models work and I said so, along
> with the explanation of why, in my very first post.
>
> >Flipper has given me a lot of guff about Thevenin and Norton;
>
> What "guff?"
Stuff to read. Reading material. Information.
Fine old guys Thevie and Norty.
One's brain falls into their lines of thought intuitively after
farnarkling around with tube circuits for long enough
and you don't even think about their theorems consciously as one plods
through a design.
Do I worry about the speed of light when I watch a sunrise?
>
> > it is
> >interesting to read the old thread, where I referred to the source
> >impedances I had calculated as ³Thevenin equivalent source impedances².
> >Jack Crenshaw complained about my use of the ³T² word, saying I was
> >merely using it to impress people by ³name dropping², and that in this
> >group it would be more appropriate for me lose the ³T² word and simply
> >refer to the ³source impedance².
>
> As I said earlier, it's always risky to take a third part description
> of someone else's comments and I'm doubly reluctant because my
> experience with you on this topic is your recollection of what I said
> bears almost no resemblance.
>
> But, judging from your claim I gave you "guff," I'd guess he suspected
> you either didn't fully get the meaning of a Thevenin output impedance
> or, in any case, that using the term was putting the cart before the
> horse because what the "output impedance" 'is' was the subject of
> discussion.
>
> I.E. Simply calculating something doesn't automatically make it a
> -->Thevenin<--- 'output impedance'.
>
> > To accommodate Jack I dropped the ³T²
> >word from my posts, however I soon had Henry on my case asking why I
> >didn't discuss the ³Thevenin source impedance² suggesting it was because
> >I didn't understand Thevenin. One can but wonder why Jack didn't take
> >Henry to task for name-dropping too?
>
> Because the whole point is that one model's 'output impedance' doesn't
> behave like a Thevenin model and the other's does. Specifically, the
> values derived in the unequal 'output impedance' model cannot be used
> like Thevenin output impedances while the value of the equal output
> impedance model can.
>
> >That old thread it is a good read and contains much other material of
> >interest, I plan to carefully read the entire thread, having quickly
> >scanned parts of it last night. I have to say thank you to Henry for
> >pointing out this wonderful old thread.
>
> I've read it and have no problem with either Henry's model or yours.
> You're the one who's bent out of shape over there being two of them.
Gee, isn't there anyone straight around here, or are they somewhat
queer?
Life is rather too short to be too serious forever.
Patrick Turner.
Patrick Turner
John Byrns wrote:
>
> In article <oJ6dnTiJCeQC5TnV...@rcn.net>,
> "Henry Pasternack" <f...@bar.com> wrote:
>
> > "Patrick Turner" <in...@turneraudio.com.au> wrote in message
> > news:48A45DBA...@turneraudio.com.au...
> > >> Henry came up with a number lower than a cathode follower and I think
> > >> Preisman did as well.
> > >
> > > I don't see how it could be lower, but I have never needed to work it
> > > out.
>
> It isn't, you have to keep in mind that you are dealing with the
> slippery fish, who in this case is misquoting Henry. Henry's original
> claim was that his CPI source impedance was lower than the source
> impedance at the cathode of the CPI when measured by the Byrns method,
> and that is indeed true, the slippery fish has incorrectly equated the
> ³Byrns² method CPI cathode source impedance with the source impedance of
> a cathode follower in his statement above.
Gee, what slippery fish? Ah Flipper?
I forgot what the Byrns method is....
But as I said in another post, the CPI aRout = kRout if loads are
constant,
and each is above Rout of a CF, 1/gm.
As you add in an anode load to a CF, the cathode Rout rises, and when
the anode load = a CCS,
the cathode Rout = the cathode load R only.
> They are not the same thing,
> the source impedance at the cathode of a CPI is higher than the source
> impedance of a cathode follower.
That's what I would think.
OK.
But my observations are that the anode output tends to sag before the
cathode output
and it affects the square wave whose shape can be made more symetrical
at top and bottom
by "tuning" with a small C across Rk.
Most makers just don't bother, because artifacts produced by not having
the C are extra 2H at above say 40kHz,
and totally unimportant.
>
> Flipper has given me a lot of guff about Thevenin and Norton; it is
> interesting to read the old thread, where I referred to the source
> impedances I had calculated as ³Thevenin equivalent source impedances².
> Jack Crenshaw complained about my use of the ³T² word, saying I was
> merely using it to impress people by ³name dropping², and that in this
> group it would be more appropriate for me lose the ³T² word and simply
> refer to the ³source impedance². To accommodate Jack I dropped the ³T²
> word from my posts, however I soon had Henry on my case asking why I
> didn't discuss the ³Thevenin source impedance² suggesting it was because
> I didn't understand Thevenin. One can but wonder why Jack didn't take
> Henry to task for name-dropping too?
>
> That old thread it is a good read and contains much other material of
> interest, I plan to carefully read the entire thread, having quickly
> scanned parts of it last night. I have to say thank you to Henry for
> pointing out this wonderful old thread.
One day I'll work out a formula for the Rout of a CPI at its a and k,
but I ain't in any hurry. I just work out what I want, a good working
point for the triode involved,
then test it all well and if it works well that's it, done like sunday
dinner.
Patrick Turner.
Patrick Turner
flipper wrote:
>
> On Thu, 14 Aug 2008 16:30:51 GMT, Patrick Turner
> 'An' Ro can be found. Whether it's useful or not is another matter and
> with an equally loaded concertina the 'classic' method you describe
> produces not only useless results but misleads people into the
> 'classic' misconception it's unbalanced.
The CPI is unbalanced if used to obtain one output voltage only.
But we force it into balance by insisting on equal loads at a and k.
Everyone knows this. As long as the test gear has very high Rin,
we will measure equal VO at a and k.
> > can be found, but sure,
> >because the Rout
> >at a and k are very different if the measurement is done by applying
> >only one same load change
> >to each a and k output, then the answer for Ro is useless.
>
> So what's the point of it?
To understand how it behaves. Human curiosity.
>
> >As I said, you could make the same load change to each of a and k, and
> >you should measure
> >equal Vchange and I change, and Ro at a and k will simply be Vchange /
> >Ichange and the same for a or k.
>
> Which is a different Ro than the ones calculated in the other case.
>
> So 'Ro' is not 'Ro' and the question becomes, which is useful?
Now I am confused.
Ro, Ro, Ro your boat along, and hope the pretty girls see you Ro-ing
down the river.
'Tis sunday here, I refuse to be serious.
>
> >> >The Vchange / I change can be used to measure Rout easily for any amp
> >> >output.
> >> >
> >> >In the case of the CPI, it can be done if you specifiy that the load
> >> >change
> >> >to anode and cathode will be equal.
> >> >Then the because the same current flows through cathode load, tube, and
> >> >anode load,
> >> >the Ichange is equal, and because the TWO loads are kept equal, V change
> >> >will also be equal,
> >> >so you'd think Rout is the same from both terminals.
> >> >
> >> >It is, but subject to conditions.
> >>
> >> Bingo... as you said, it *is* (the same).
> >>
> >> So why were you chastising folks for saying exactly what you just
> >> said?
> >
> >Because of the condition of the test for Rout that needs to be
> >specified.
> >
> >Conditions apply for the truth to be true.
>
> The conditions have always been specified, over and over and over and
> over and over and over and over and over and over and over....
>
> So your 'explanation' is invalid.
Really?
> No one said otherwise.
>
> >> They just aren't the same thing, which is why measuring it as one
> >> thing doesn't give you the same answer as measuring it when it's the
> >> other.
> >
> >The concertina to my mind is merely a common cathode stage with a lot of
> >local current FB from
> >its unbypassed Rk.
> >
> >OK, so you take outputs from both a and k.
> >
> >It doesn't stop the concertina being a common cathode amp.
>
> Nothing stops you from changing any topology but, if you do, it isn't
> the same topology.
>
> And the proof to the pudding here is the different values for 'Ro'
> you, yourself. know one gets if you use it one way vs the other.
>
> Frankly, Pat, you're tilting at windmills and just being obstinate
> because *you* agree the output impedances are equal under the defined
> conditions, which have *always* been stated. You have no complaint
> despite complaining for nothing more than the sake of complaining.
But that's what everyone else seemed to be doing around here.
Its the style, the agony, that hooks me right in.
Peer group pressure at work.
I must try to resist it.
>
> >> >> >And you'll find the cathode is a voltage source, ie, Rout < RL at the
> >> >> >cathode,
> >> >> >and Rout at the anode is a current source, ie, Rout > RL at the anode.
> >> >>
> >> >> You're not measuring a concertina.
> >> >>
> >> >> >Now this is true of any common cathode amplifier with an unbypassed Rk,
> >> >> >and you test the Rout at
> >> >> >anode and cathode separately.
> >> >>
> >> >> That's right, a common cathode amplifier, not a concertina.
> >> >
> >> >As I said, a concertina *is* a common cathode amp......
> >>
> >> No it is *not*. It looks a hell of a lot like one but a common cathode
> >> amplifier has ONE output and a concertina has TWO, with equal loads.
> >
> >
> >So what about the number of outputs?
> >
> >Its still a basic common cathode amp.
>
> You know better than to argue 'just one thing' doesn't make any
> difference and, in a conventional amp, all it takes is 'just one
> resistor' from output to cathode to 'change Ro'.
>
> Go ahead, a GNFB amp both with and without the 'one thing' and then
> ask me "so what?:
>
> >Another way to get phase inversion is to simply use a common cathode amp
> >with
> >a gain of exactly -1.0, ie, a triode common cathode amp is set up with
> >an unbypassed Rk
> >which is slightly lower in value than the RLa, and Vg = -Va.
> >
> >So you have the input signal from somewhere external, maybe a CD player,
> >and you create an opposite
> >phase signal of exactly the same amplitude, and the two phases can then
> >be applied to a fully
> >balanced PP power amp with balanced series voltage GNFB. ARC did this
> >maybe 30 years ago.
> >
> >The word "Concertina" does not make it illegal to say the concertina is
> >a common cathode amp.
> >It is a common cathode amp, but one with special features, implied by
> >the word concertina.
>
> See? You can't even make the argument without saying "special" and
> invoking a different 'name' for it.
>
> To use your own admonition, 'build one' and 'make measurements'. And
> if you measure it the way it is *used*, with balanced loads, you'll
> find equal output impedances.
> I haven't calculated it either. All I said is Henry did.
>
> I don't find it difficult to imagine, though, because the same
> mechanism that reduces anode output impedance, load 'feedback', is at
> work on the cathode.
>
> Seemed to me it wouldn't be 'much' but Henry said it was a fair
> amount, which is why I remembered it.
>
> >> >Math experts should have come up with all the releveant figures by now,
> >> >but I've never
> >> >*needed* to calculate the Rout, so I have never have.
> >>
> >> That's ok. It doesn't mean someone else doesn't care, though.
> >
> >Hmm, we have not seen too much care around here and have not seen
> >anyone say what the Rout actually is for CPI if a&k loads are always the
> >same.
>
> Well, you were criticizing without bothering to know what was said and
> by who, then, because I explained in my very first post why I 'cared'.
The root and soul of the matter could be expressed in math so that
less time is wasted on endless discussions and more time is available
for soldering and
being useful.
If I seem to be aloof its because ppl are yardi yardi ya all day and
I don't have time to concentrate on each atom of information, and each
tiny grain
of upset emotion.
>
> >> Just knowing they're equal, never mind the 'value', would have saved a
> >> hell of a lot of confusion over the last century, though.
> >>
> >> >> >The only way to ensure the CPI has equal Rout at a and k would be to
> >> >> >direct couple
> >> >> >a pair of cathode followers to cathode and anode, and then you'd find
> >> >> >the two Routs would be the same
> >> >> >and each would be equal to what you'd get with any CF.
> >> >>
> >> >> There is no need because if one defines 'output impedance' per the
> >> >> Thevenin model then a concertina already has equal Thevenin 'output
> >> >> impedances' as long as the loads are equal.
> >> >
> >> >"as long as the loads are equal" is the condition needed for equal Rout
> >> >at each terminal.
> >> >
> >> >What if they were not in a dynamic working amp?
> >>
> >> Doesn't matter as long as the load impedances are equal,
> >
> >Well there is a point where the loads suddenly do become unequal, at
> >grid current
> >in a following stage.
> >
> >As one phase goes +, it hits and stalls with Ig, but the other phase
> >going -
> >has no grid current.
> >
> >Guess which output tends to charge up the coupling caps the most.
>
> None of the models work if the circuit leaves linear operation and
> THAT is another stated condition.
>
> It's also a stated condition for the Thevenin model and what you call
> 'Ro'.
> I wasn't building an amp with that. I was building one with a
> Concertina.
> That's great.
>
> Still has nothing to do with the Ro discussion.
I've given a simple method to measure the a and k Routs.
C affects CPI, and I sure don't have the math on how it does,
but AF amp HF response is affected by C in the tube circuits.
>
> >> >> Which resolves the century old befuddlement of why the damn thing
> >> >> works despite those confounding 'different impedances' that had even,
> >> >> so called, 'experts' shoving 'build out resistors' on the thing to
> >> >> solve a problem with those confounding 'different impedances' that
> >> >> didn't exist.
> >> >>
> >> >> You simply accept that it works, despite the 'different impedances'. I
> >> >> have shown *why* it works and done so three ways: with the 'one
> >> >> current through equal loads' derivation and two models, one with your
> >> >> preferred unequal 'output impedances' (measured with a broken
> >> >> concertina) and one with the equal Thevenin equivalent output
> >> >> impedances.
> >> >
> >> >I might have said more stuff than "it just works."
> >>
> >> Well, you usually say 'more stuff'. Whether it's related to the topic
> >> is another question and it's true I haven't heard everything you've
> >> ever said.
> >>
> >> But this last time around you didn't say anything about how in the
> >> world different impedances into equal capacitive loads could possibly
> >> come out with an equal roll off. All you said was the unequal
> >> impedances don't stop it from working just fine.
> >
> >
> >
> >>
> >> Well, as you said above, the reason is the output impedances *are*
> >> equal, not different.
> >
> >Well, I suggest you examine a working amp more closely.
>
> I already did. They're equal.
To be equal they depend on equal loading.
At HF the C affects the CPI adversely.
HF roll off poles occurs at different F unless trimming C are placed.
>
> And you said so as well, so I suggest you argue with yourself about
> it.
>
> >You might find the reason why some makers add a C across Rk of a CPI.
> >
> >Its to slightly boost the anode output which sags before the cathode
> >output.
> >
> >Most makers don't bother, like they don't bother to do a whole range of
> >stuff
> >because they work down to a price, not up a standard of quality.
>
> That's nice. It still has nothing to do with the Ro discussion.
!
> You can babble that nonsense till you're blue in the face but I've
> been there, done that, got the T-Shirt, know what the hell I'm talking
> about.
>
> Bean counters count beans. That's why they're called bean counters.
Ah, you got a T-Shirt!
Wow, I never knew that. Fantabulous news.
Bean counters also count dollars, and screws, and nuts, and tubes and
sockets,
and millimetres. Acording to them, all such things they count must come
to low totals.
>
> <snip of Pat showing he doesn't understand business>
I undertsand it very well. Business doesn't understand me.
If everyone was like me there'd be no bean counters.
No need. Ppl would make things adequately well without these parasitic
bastards.
Natural competion would still function and be accepted, but bean
counters bring unatural competition into
every thing they touch, and they symbolise the greed of the world.
Bean counters = efficiency overdose.
Business likes to get everything it can made in China because some bean
counter
said its far cheaper than employing YOU.
As a result, all manner of cheap gadget arrive by boat, and everyone
marvels and gets sucked in.
But oops, the greenhouse effect is ruining the Dream, but western
BUSINESS people
have no conscience troubles with Chinese working like slaves on $2 per
day,
and what's more, the western business ppl won't even give the Chinese an
extra $1 per day
to clean up their emmisions, and all the environmental damage they are
doing in China and around the world.
Things could have been worse, and the standards of living could have
remained at 1955 standards,
and with the really high CO2 emissions of that era, where americans
drove cars with appalling thirst for gas.
But reducing CO2 a lot is offset by population increase, and the fact
that 4 billion ppl
now want equal lifestyles to YOU.
So in 100 years there won't be much rain forest, everything minable will
have been mined,
there won't be any lions, tigers, elephants left, the world's oceans
will be fouled,
food will be hard to grow, and I guess everyone will fight it out over
what's left
to fight over, and the temperature will be +5C, and the waters will be
flooding major cities,
and we won't feel like re-building them all so soon.
There will be lots of mosquitoes though.
Sorry to be pessimistic, but I see a lot of doom and gloom ahead because
of business.
Business simply represents human nature.
When things get real bad, people won't be able to breed so easy.
But here in Oz, much of generation Y is postponing family life
indefinately,
because they see the writing on the wall, and they see a house costs 1/5
a million at least,
and they can't get job security. Their parents live far too long so they
never
see their inheritance until they are old as well.
Maybe in 100 years we'll have learnt to genetically modify ourselves to
cope a bit better,
like removing the gene for depression for starters. And to breathe in
C02, and breathe out 02.
And to eat garbage. The garbage pile from humans is getting big, but its
nothing much compared
to what it'll be in 100 years. So the best thing the bean counters can
achieve is to
force engineers to design people to eat it. Cheaper than growing new
food.
Same old solutional thinking.
Doctors will need to addapt to keeping genetically altered humans alive
at the right price of course.
Don't worry, Be happy, doom is a hundred years away, and you and I will
be long gone. Not our problem.
Somebody eles's!
Patrick Turner.
Patrick Turner
Thanks for taking us all backwards to 2001 where it wasn't such a
terrible place,
and there was some good figuring outing going on.
From the above reference, you had a triode in CPI with Ra = 1k, µ = 10,
and RLa = RLk = 10k.
( Could be nearly like a EL86 in triode )
From that you reckoned Rout of each output under equal loading
conditions = 82.6 ohms.
OK, now for the triode, cathode follower Rout = 1 / gm , and gm = µ / Ra
= 10 / 1,000 A/V = 10mA/V.
So a CF with such a tube would have Rout = 1 / 0.01 = 100 ohms, slightly
higher than the 82.6 ohms
you calculated with CPI.
If the CF already has a dc carrying cathode load of 10k, it is in
parallel with the tube Rout, but the
difference is so great the 10k makes negligible Rout difference.
So what would happen when you add an anode load?
What if you had a CCS as the anode load?
There would be no change to the tube current.
If the grid goes up 1V, the cathode voltage won't move. All the voltage
movement will be at the anode.
In fact anode voltage will be -10V, for +1V at the grid. Since no
current change occurs in the triode
because of the CCS anode supply, there cannot be any change to cathode
load voltage.
So any external load connected to the cathode would find Rout at the k =
10k, ie, the cathode load R.
So methinks as any load is introduced into the anode circuit of a CF,
the cathode Rout
begins to go higher than a pure CF.
In other words, for the lowest Rout possible from a cathode, you have to
completely omit any anode load.
Don't quote me on this, I'll need to check a circuit out and make tests
of my own with a real
triode in a CPI set up and with tests done by varying both cap coupled
anod and cathode loads
so that the loads stay equal.
Its one thing to post lofty math, but to be really true there has to be
a verifying experiment.
The perception of output resistance of other phase inverters such as the
long tail pair
also needs to be specified for the conditions.
Say you have two triodes each with Ra = 10k such as 6SN7.
When you measure the Rout at just one anode of the pair, you'll get
Rout much higher than Ra, because the cathode of that triode has the
common cathode current sink
resistor, and the cathode input resistance of the other triode as its
unbypassed cathode resistance.
But suppose you load the LTP with an additional load resistance from
anode to anode, or two equal R
with each cap coupled to 0V.
Then you should find Rout = Ra at each anode.
My 2C.
Patrick Turner.
John Byrns
flipper <fli...@fish.net> wrote:
> On Fri, 15 Aug 2008 13:01:41 -0500, John Byrns <byr...@sbcglobal.net>
> wrote:
>
> >In article <oJ6dnTiJCeQC5TnV...@rcn.net>,
> > "Henry Pasternack" <f...@bar.com> wrote:
> >
> >> "Patrick Turner" <in...@turneraudio.com.au> wrote in message
> >> news:48A45DBA...@turneraudio.com.au...
> >> >> Henry came up with a number lower than a cathode follower and I think
> >> >> Preisman did as well.
> >> >
> >> > I don't see how it could be lower, but I have never needed to work it
> >> > out.
> >
> >It isn't, you have to keep in mind that you are dealing with the
> >slippery fish, who in this case is misquoting Henry.
>
> I've tried to stay cordial but if hurling insults is your opinion of
> the 'good way' to make a case then let me know because, in the spirit
> of collegial accommodation, I'll gladly hurl a few grenades your way
> if it'll make you happy.
Sorry to be so long in getting back to you but I was away at the beach
for three days and it has taken me all day to recover from this little
"vacation".
Your silly fish name, and your anonymous posting habit, make it hard to
respect you. The "empty calories" you have been posting in this thread
don't help much. Your constant references to Thevenin and Norton in
attempts to criticize my posts without any indication of their actual
relevance to my posts is a constant irritant. You also spoke of
checking your 13FD7 amplifier, yet I never saw the results of any
impedance measurements posted.
Throw some grenades my way if it will make you feel better, I don't
mind, it seems unlikely you will ever be able to equal the gang during
the "Wars", who even went so far as to hurl insults at my wife.
I am making a modest effort at improving my attitude towards Henry, but
don't forget that he has called me far more names during and since the
"War" than I have ever called him.
> >> And yet it is true. In fact, for an example I calculated, the equal-load
> >> effective output impedance was an order of magnitude lower than the
> >> cathode-only output impedance. Read about it here:
> >>
> >> http://groups.google.com/group/rec.audio.tubes/msg/3f5394ad0426aeb1
> >>
> >> Consider the case where you infer output resistance by measuring the
> >> -3dB point when driving a capacitive load. With a single capacitor at
> >> the cathode you will get one result. Now, adding an identical capacitor
> >> at the plate will reduce the cathode output impedance because it bypasses
> >> the plate resistance.
> >
> >I'm not sure why you are getting into the capacitor business,
>
> Because it's a valid means of measuring the circuit despite your
> confusion about it.
You missed my point, my point was that the capacitive load was
unnecessary to demonstrate his point which was already illustrated in
the post he referenced, without the need for a capacitive load.
> >There is a lot of other interesting stuff in the thread. There is a
> >discussion of my anode and cathode transfer functions, and how they
> >degenerate into a form identical to Henry's when you make the anode and
> >cathode load impedances equal, as in a well balanced concertina.
> >Another interesting point is where I ³Aced² what I will call the
> >³Flipper² challenge.
>
> Oh? And just what is the ³Flipper² challenge?
The "Flipper" challenge is my new name for the "Pasternack" challenge of
2001. Back in 2001 Henry challenged me to calculate the -3 dB point of
a CPI using my CPI equations, while you aske3d me a week or so ago how
the "RC time constant" of the CPI could be calculated with my CPI
equations. It is pretty much the same challenge.
> I.E. Simply calculating something doesn't automatically make it a
> -->Thevenin<--- 'output impedance'.
Can you give a clear definition of what makes something a
"-->Thevenin<--- 'output impedance'"?
> I've read it and have no problem with either Henry's model or yours.
> You're the one who's bent out of shape over there being two of them.
I have two problems, first it isn't obvious to me that Henry's method is
a valid source impedance measurement, what he is measuring is the source
impedance between the cathode and anode driving a balanced load, and
then assuming that half that source impedance is attributable to the
cathode and half to the plate. It isn't obvious to me that that is a
valid assumption.
The second problem I have is that if there are "two of them" how do we
know that there aren't really three or four or more "models" for the
source impedance? Can we choose any arbitrary value for the source
impedance that we want to?
John Byrns
Patrick Turner <in...@turneraudio.com.au> wrote:
> John Byrns wrote:
> >
> > In article <oJ6dnTiJCeQC5TnV...@rcn.net>,
> > "Henry Pasternack" <f...@bar.com> wrote:
> >
> > > "Patrick Turner" <in...@turneraudio.com.au> wrote in message
> > > news:48A45DBA...@turneraudio.com.au...
> > > >> Henry came up with a number lower than a cathode follower and I think
> > > >> Preisman did as well.
> > > >
> > > > I don't see how it could be lower, but I have never needed to work it
> > > > out.
> >
> > It isn't, you have to keep in mind that you are dealing with the
> > slippery fish, who in this case is misquoting Henry. Henry's original
> > claim was that his CPI source impedance was lower than the source
> > impedance at the cathode of the CPI when measured by the Byrns method,
> > and that is indeed true, the slippery fish has incorrectly equated the
> > ³Byrns² method CPI cathode source impedance with the source impedance of
> > a cathode follower in his statement above.
>
> Gee, what slippery fish? Ah Flipper?
>
> I forgot what the Byrns method is....
It's the equations I developed to define the elemental "CPI" which are presented
a few paragraphs further down.
> But as I said in another post, the CPI aRout = kRout if loads are
> constant,
> and each is above Rout of a CF, 1/gm.
Isn't Rout for a CF equal to rp/(u+1)? IIRC Henry's Rout for both the anode and
cathode terminals of the CPI is rp/(u+2), which is always lower than Rout for a
CF using the same tube.
[Snip]
> One day I'll work out a formula for the Rout of a CPI at its a and k,
> but I ain't in any hurry. I just work out what I want, a good working
> point for the triode involved,
> then test it all well and if it works well that's it, done like sunday
> dinner.
No need to bother, the dinner has already been cooked and is on the table below.
The equivalent generator impedance at the cathode of the concertina is:
(1) Zgk = (rp + Zp) / (u + 1)
The equivalent generator Voltage at the cathode of the concertina is:
(2) egk = es * u / (u + 1)
Combining 1 & 2 with Zk the load Voltage at the cathode of the concertina is:
(3) ELk = es * (u / (u + 1)) * Zk / ((rp + Zp) / (u + 1) + Zk)
Rearranging equation 3 we get:
(4) ELk = es * u * Zk / (rp + (u + 1) * Zk + Zp)
The equivalent generator impedance at the plate of the concertina is as follows:
(5) Zgp = rp + (u + 1) * Zk
The equivalent generator Voltage at the plate of the concertina is as follows:
(6) egp = es * u
Combining 5 & 6 with Zp the load Voltage at the cathode of the concertina is:
(7) ELp = es * u * Zp / (rp + (u + 1) * Zk + Zp)
The meaning of the symbols in the above equations is as follows:
es is the source Voltage at the input of the concertina circuit
rp is the plate resistance of the tube (valve) in the concertina circuit
u is the amplification factor of the tube (valve) in the concertina circuit
Zp is the load on the concertina plate, including the plate resister
Zk is the load on the concertina cathode, including the cathode resister
Zgp is the generator source impedance at the plate terminal of the concertina
Zgk is the generator source impedance at the cathode terminal of the concertina
egp is the generator source Voltage at the plate terminal of the concertina
egk is the generator source Voltage at the cathode terminal of the concertina
ELp is the load Voltage at the plate terminal of the concertina
ELk is the load Voltage at the cathode terminal of the concertina
Notice that equation 4 for the Voltage across the cathode load is identical with
equation 7 for the Voltage across the plate load, with the exception Zk in the
numerator of eq 4, and Zp in the numerator of equation 7. If the loads on the
concertina, Zk and Zp, are equal, then the output Voltages at the plate and
cathode are equal. This is true even though the source impedance at the cathode
terminal, given by equation 1, and the source impedance at the plate, given by
equation 5, are nowhere near equal.
The RC time constant determining the -3 dB rolloff point when Zk equals Zp can
be calculated from the pole location in equation 7, by replacing Zk and Zp with
the parallel combination of Rl and Cl, giving TC = ((rp/(u +2))||Rl) * Cl.
The Phantom
wrote:
>In article <48A70CF2...@turneraudio.com.au>,
typo here; should be: ^^^^plate^^^^
There should probably be a minus sign in here somewhere:
>(7) ELp = es * u * Zp / (rp + (u + 1) * Zk + Zp)
So it should be:
(7) ELp = -es * u * Zp / (rp + (u + 1) * Zk + Zp)
The Phantom
wrote:
<SNIP>
>>
>> Could you elaborate on what the goof was?
>
>The goof was not a typo or an error in a formula, his idea of placing a
>build out resistor in the cathode of a concertina phase inverter to
>equalize the source impedances of the plate and cathode circuits was
>simply a goofy idea. It was a "bright" idea intended to fix an imagined
>problem that didn't actually exist, that instead created a real problem.
>
>I saw the magazine article
I'm posting the page from the magazine article where he shows a schematic
"...featuring--possibly for the first time--cathode build-out resistor in
the driver stage.", and several letters that followed.
It's over on ABSE.
>and the first edition of his book where he
>presented this goofy idea, I have never seen the second edition of his
>book to see how he extricated himself from the predicament he created
>for himself, although I have been told by people that have seen the
>second edition that he did somehow extricate himself.
John Byrns
The Phantom <pha...@aol.com> wrote:
Hi Rodger,
Thanks for pointing out these errors, you are clearly far and away the Ace
proofreader in the group. I am absolutely amazed that neither Henry nor Flipper
noticed these errors as they both had approved the equations without noting the
errors. I assume they missed the minus sign error because it wasn't
particularly relevant to the argument at hand.
I guess the discovery of these errors vindicates my original warning when I
first posted these equations, that they ³may contain many typos.²
You did miss the error in equation 6 which should probably also contain a minus
sign as in equation 7. The omission of the minus sign in equation 6 was
obviously the root cause of the missing minus sign in equation 7, which is the
result of combining equations 5 & 6.
John Byrns
The Phantom <pha...@aol.com> wrote:
> On Tue, 05 Aug 2008 13:04:52 -0500, John Byrns <byr...@sbcglobal.net>
> wrote:
>
> <SNIP>
> >>
> >> Could you elaborate on what the goof was?
> >
> >The goof was not a typo or an error in a formula, his idea of placing a
> >build out resistor in the cathode of a concertina phase inverter to
> >equalize the source impedances of the plate and cathode circuits was
> >simply a goofy idea. It was a "bright" idea intended to fix an imagined
> >problem that didn't actually exist, that instead created a real problem.
> >
> >I saw the magazine article
>
> I'm posting the page from the magazine article where he shows a schematic
> "...featuring--possibly for the first time--cathode build-out resistor in
> the driver stage.", and several letters that followed.
>
> It's over on ABSE.
Just as a point of interest a large number of US residents, myself included, no
longer have access to these binary groups as a result of the New York AGs
actions.
The Phantom
wrote:
I didn't miss it. I figured I would give you one freebie. :-)
>The omission of the minus sign in equation 6 was
>obviously the root cause of the missing minus sign in equation 7, which is the
>result of combining equations 5 & 6.
Yep, I saw that, but I thought I would just point it out at the final
expression.