Any problems with plugging an 8ohm speaker out into a 16 ohm cab?
Nick V. Flor
speaker cab, does that hurt my amp in any way? I'm just assuming that it
won't be as loud as plugging into an 8-ohm cab. Is this true? Anything
else I should worry about?
Thanks,
- Nick
PMG
amp, that if your speaker has more ohms than the amp specifies, then you
are safe (so you'd be ok, if it's a tube amp). The problem would be if
you tried to use less ohms than the amp wanted.
Pete
--
Of course I can talk,
I'm a monster, not a mime --Whackhammer
D.E. Tilmans
Nick V. Flor <guitar...@worldnet.att.net> schreef in berichtnieuws
gaLb5.5305$tI4.3...@bgtnsc05-news.ops.worldnet.att.net...
tubegod
state, the same rules apply. Always make sure your overall
cabinet impedence equals, or is more than, the amps'expected
impedence.
-----------------------------------------------------------
Got questions? Get answers over the phone at Keen.com.
Up to 100 minutes free!
http://www.keen.com
Count Scrofula
(which I would bet you plan to do since you are jamming into a cab)
But--a mismatched load may alter the frequency response of the amp, sucking
tone and cuasing it to sound like crap.
I do not recommend. You may be able to rewire the cab to present a proper
load to the amp, which may be your best option.
PMG <av...@mediaone.net> wrote in message
news:396F86A1...@mediaone.net...
> I was told by what I'd consider a reliable source, that with a _tube_
> amp, that if your speaker has more ohms than the amp specifies, then you
> are safe (so you'd be ok, if it's a tube amp). The problem would be if
> you tried to use less ohms than the amp wanted.
>
> Pete
>
> "Nick V. Flor" wrote:
> >
> > I have an amp head with an 8-ohm speaker out. If I plug that into a 16
ohm
> > speaker cab, does that hurt my amp in any way? I'm just assuming that
it
> > won't be as loud as plugging into an 8-ohm cab. Is this true? Anything
> > else I should worry about?
> >
> > Thanks,
> >
> > - Nick
>
PMG
tone, it muddies it up some. But it's safe, you don't need to worry
about cranking it, unless you're worried about the durability of your
speaker. Just provide your amp with greater than or equal to the ohms
it's asking for, and you're ok.
Sure, rewiring your speaker cabinet would be a good option if it has 2
or 4 speakers.
Pete
Lord Valve
fulla shit. That's back-asswards.
LV
Kent Pearson
point out that this is not the first person who's been given this exact same
misinformation. I've also heard the same thing from various sources for
years now, namely that higher impedance was ok but that lower was disaster.
Where do wive's tales originate??? How are us guitar players supposed to
keep everybody's stories straight?
- KP
Kent Pearson
On 15-Jul-2000, PMG <av...@mediaone.net> wrote:
> And actually, I'd like to hear more about the history of the amps with
> the fried sockets, tubes, capacitors, and xformers. Are we talking
> about amps that were running at 10 for 4 & more hours a day? Are we
> talking about amps that had extreme mismatches in the speaker
> impedance? Are these people who were using 16 or 32 or worse ohm
> speakers in an 4 ohm amp, or are we talking about people who used 8ohms
> into a 4ohm amp?
Exactly. I've done this many many times over the years with no apparent
problems. Of course, it MUST happen or else we wouldn't be talking about
it. And I certainly wouldn't recommend to anyone. It just that it's never
happened to *me* in all these years. I guess some amps may be more
"durable" (for lack of a better word) than others. Is it possible to fuse
protect against the ill effects described in the quote as being possible
from (accidental) mismatch?
- KP
- KP
Kent Pearson
- KP
Kent Pearson
On 15-Jul-2000, Tom <tma...@erols.com> wrote:
> The answer is simple: Trust in the Lord.
Testify, Brother Tom!
- KP
Lord Valve
> Regardless whether or not your power amp is a tube or solid
> state, the same rules apply. Always make sure your overall
> cabinet impedence equals, or is more than, the amps'expected
> impedence.
>
Lord Valve Speaketh:
Hey, god...
You done stepped on yer pecker, son. Loading a tube
amp with a higher impedance than the tranny is looking
for can cause flyback. This will fry sockets, tubes,
and sometimes HV capacitors and even output transformers.
I've even seen the filament winding in a power tranny
croak from this, since that's where the juice goes when
it leaves the plate circuit. Maybe ya better change
yer screen name to "sandgod;" your advice sounds like
it was hatched in Silicon Valley. If you have to run
a mismatched load with a tube amp, lower is better
than higher. Check Deja for details, this one's been
done to death for the last 5 years. So Sayeth the Lord.
Lord Valve
VISIT MY WEBSITE: http://www.freeyellow.com/members2/lord-valve/
Good tube FAQ for newbies. Click the e-mail link and join my
SPAM LIST; just put "SPAM ME" in the header and I'll sign you
up. (If you only want a set of e-mail catalogs, put "CATS ONLY"
in the header.) I specialize in top quality HAND-SELECTED NOS and
current-production vacuum tubes for guitar and bass amps. Good
prices, fast service. TONS of gear and parts in stock...let's DEAL!
NBS Electronics, 230 South Broadway, Denver, CO 80209-1510
Phone orders/tech support after 1:00 PM Denver time at 303-778-1156
NOW ACCEPTING VISA AND MASTERCARD
CHAT WITH LORD VALVE: Log onto any DALnet server and join
channel #CONELRAD. Look for me there most any night after
11:00 PM Denver (Mountain) time. Guitar-amp questions and
what-have-you are welcome.
"It ain't braggin', if ya can do it." - Babe Ruth
Lord Valve
LV
PMG wrote:
> I was told by what I'd consider a reliable source, that with a _tube_
> amp, that if your speaker has more ohms than the amp specifies, then you
> are safe (so you'd be ok, if it's a tube amp). The problem would be if
> you tried to use less ohms than the amp wanted.
>
> Pete
>
> "Nick V. Flor" wrote:
> >
> > I have an amp head with an 8-ohm speaker out. If I plug that into a 16 ohm
> > speaker cab, does that hurt my amp in any way? I'm just assuming that it
> > won't be as loud as plugging into an 8-ohm cab. Is this true? Anything
> > else I should worry about?
> >
> > Thanks,
> >
> > - Nick
>
Ned Carlson
>I was told by what I'd consider a reliable source, that with a _tube_
>amp, that if your speaker has more ohms than the amp specifies, then you
>are safe (so you'd be ok, if it's a tube amp).
Willie is right, this is bass-ackwards.
The problem would be if
>you tried to use less ohms than the amp wanted.
>
>Pete
Oye,Pedro, you been reading a different newsgroup?
>"Nick V. Flor" wrote:
>>
>> I have an amp head with an 8-ohm speaker out. If I plug that into a 16 ohm
>> speaker cab, does that hurt my amp in any way? I'm just assuming that it
>> won't be as loud as plugging into an 8-ohm cab.
Pray tell, *what* amp into *what* cab, using what speakers?
Are we supposed to *guess* this?
Really, how in fuck-all is anyone going to give you an intelligent
answer, if you don't tell us.
Ned Carlson Triode Electronics "where da tubes are!"
2225 W Roscoe Chicago, IL, 60618 USA
ph 773-871-7459 fax 773-871-7938
12:30 to 8 PM CT, (1830-0200 UTC) 12:30-5 Sat, Closed Wed & Sun
<A HREF="http://www.triodeel.com">http://www.triodeel.com</A>
Tube and Tube Amp info on the net...<A HREF="http://www.triodeel.com/tlinks.htm"> The Big Tube Links Page!</A>
PMG
the fried sockets, tubes, capacitors, and xformers. Are we talking
about amps that were running at 10 for 4 & more hours a day? Are we
talking about amps that had extreme mismatches in the speaker
impedance? Are these people who were using 16 or 32 or worse ohm
speakers in an 4 ohm amp, or are we talking about people who used 8ohms
into a 4ohm amp?
I started looking for a way to cross check this info other than using
deja archives, but I need to look around some more, I'm not finding the
info yet.
Pete
Kent Pearson wrote:
>
> I'm not doubting LV at all, I know far less about it. But LV, I have to
> point out that this is not the first person who's been given this exact same
> misinformation. I've also heard the same thing from various sources for
> years now, namely that higher impedance was ok but that lower was disaster.
> Where do wive's tales originate??? How are us guitar players supposed to
> keep everybody's stories straight?
>
> - KP
>
> On 15-Jul-2000, Lord Valve <detr...@ix.netcom.com> wrote:
>
> > Call whoever told you that and tell 'em Lord Valve sez they're
> > fulla shit. That's back-asswards.
> > LV
> >
> > PMG wrote:
> >
> > > I was told by what I'd consider a reliable source, that with a _tube_
> > > amp, that if your speaker has more ohms than the amp specifies, then you
> > > are safe (so you'd be ok, if it's a tube amp). The problem would be if
> > > you tried to use less ohms than the amp wanted.
> > >
> > > Pete
> > >
> > > "Nick V. Flor" wrote:
> > > >
> > > > I have an amp head with an 8-ohm speaker out. If I plug that into a
> > > > 16 ohm
> > > > speaker cab, does that hurt my amp in any way? I'm just assuming that
> > > > it
Count Scrofula
Ned Carlson <postm...@triodeel.com> wrote in message
*SNIP*
>
> The problem would be if
> >you tried to use less ohms than the amp wanted.
> >
> >Pete
>
> Oye,Pedro, you been reading a different newsgroup?
>
It's that new group, alt.guitar.amp.solid.state
Tom
Regards.
Kent Pearson wrote:
>
> I'm not doubting LV at all, I know far less about it. But LV, I have to
> point out that this is not the first person who's been given this exact same
> misinformation. I've also heard the same thing from various sources for
> years now, namely that higher impedance was ok but that lower was disaster.
> Where do wive's tales originate??? How are us guitar players supposed to
> keep everybody's stories straight?
>
> - KP
>
> On 15-Jul-2000, Lord Valve <detr...@ix.netcom.com> wrote:
>
> > Call whoever told you that and tell 'em Lord Valve sez they're
> > fulla shit. That's back-asswards.
> > LV
> >
> > PMG wrote:
> >
> > > I was told by what I'd consider a reliable source, that with a _tube_
> > > amp, that if your speaker has more ohms than the amp specifies, then you
> > > are safe (so you'd be ok, if it's a tube amp). The problem would be if
> > > you tried to use less ohms than the amp wanted.
> > >
> > > Pete
> > >
Nick V. Flor
Thanks, btw.
- Nick
"Ned Carlson" <postm...@triodeel.com> wrote in message
tubegod
an overall impedence of 4ohms, which is described as being a
heavier load than 8ohms because the amp has to come up with more
current,I'd be better off? Hmm, I guess I should call all the
publishers of electronics refernce materials and give them your
number...
Simply Steve
Lord Valve wrote:
> tubegod wrote:
>
> > Regardless whether or not your power amp is a tube or solid
> > state, the same rules apply. Always make sure your overall
> > cabinet impedence equals, or is more than, the amps'expected
> > impedence.
> >
>
> Lord Valve Speaketh:
>
> Hey, god...
> You done stepped on yer pecker, son. Loading a tube
> amp with a higher impedance than the tranny is looking
> for can cause flyback. This will fry sockets, tubes,
> and sometimes HV capacitors and even output transformers.
> I've even seen the filament winding in a power tranny
> croak from this, since that's where the juice goes when
> it leaves the plate circuit. Maybe ya better change
> yer screen name to "sandgod;" your advice sounds like
> it was hatched in Silicon Valley. If you have to run
> a mismatched load with a tube amp, lower is better
> than higher. Check Deja for details, this one's been
> done to death for the last 5 years. So Sayeth the Lord.
>
> Lord Valve
A-fucken-men! Everytime this question comes up and I've replied with the
same basic answer I've been told I'm wrong and people come up with all
sorts of oddball scenarios to prove it.
Thanks,
Steve
Simply Steve
Before I bought new spkrs for my Vibrolux Reverb all I had were 4 ohm 10" spkrs,
The VR calls for a 4 ohm load, I asked LV which was better and he told me to wire
em up for 2 ohms, I did and gigged HEAVILY (read every weekend and then some) that
way with the amp for almost a year. No damage. In fact I am still using the same
tubes.
I know that's not the type of history you asked for...
Steve
PMG wrote:
> And actually, I'd like to hear more about the history of the amps with
> the fried sockets, tubes, capacitors, and xformers. Are we talking
> about amps that were running at 10 for 4 & more hours a day? Are we
> talking about amps that had extreme mismatches in the speaker
> impedance? Are these people who were using 16 or 32 or worse ohm
> speakers in an 4 ohm amp, or are we talking about people who used 8ohms
> into a 4ohm amp?
>
> I started looking for a way to cross check this info other than using
> deja archives, but I need to look around some more, I'm not finding the
> info yet.
>
> Pete
>
Stefan Markowitz
tubegod schrieb in Nachricht
<156047c2...@usw-ex0105-038.remarq.com>...
>So you are saying if my amp is looking for 8ohms and I hook up
>an overall impedence of 4ohms, which is described as being a
>heavier load than 8ohms because the amp has to come up with more
>current,I'd be better off? Hmm, I guess I should call all the
>publishers of electronics refernce materials and give them your
>number...
If you are in doubt about LV“s statement, why don“t you just try it?
Crank up your tube amp without a speaker connected. If you were
right, the amp would not be damaged. (No load, no current, why
should it be damaged? :-) )
Hmm, when I think about, if I do that with my Dynacord Reference amp,
nothing happens.
Guess what: the speaker out connector shorts the output when there is no
cable plugged in in order to protect the amp. Do you think the engineer
who designed this was an idiot?
Remember, we are talkin“bout tube amps, not solid state!
Stefan
Nick V. Flor
the reason I was asking is that I recently finished building a tube amp kit
(Torres Tiny Tone, 2-12ax7s, 1-6005, 1.5W Amp), and I had the option of
wiring it up for 4, 8 or 16 ohms. I have a Tone Master 2x12 cab with
Vintage 30s in it, and that's 16 ohms.
However, it seems like most cabs are 8ohms, so I just wired it up for 8
ohms. I asked AGA my question cuz I wanted to know if I was damaging my amp
by hooking it up to the ToneMaster cab.
Looks like the answer is yes.
But I'm still curious about my other question. Okay, suppose you do have an
amp set up for 16-ohms and you hook up an 8-ohm cab. What kind of
differences in tone do you get compared to hooking up a 16-ohm cab?
Thanks again,
- Nick
Duncan Munro
<Delt...@Xma.freei.netX> wrote:
>I'm not doubting LV at all, I know far less about it. But LV, I have to
>point out that this is not the first person who's been given this exact same
>misinformation. I've also heard the same thing from various sources for
>years now, namely that higher impedance was ok but that lower was disaster.
Kent, it's not quite as easy as that :-(
* Lower impedance will _generally_ stress the power tubes gradually
more and more as the volume goes up.
* Higher impedance will _generally_ stress the power tubes less as the
volume goes up until the powertubes cut off at high volume levels.
This will create voltage spikes on the plates of the power tubes
called flyback.
If the flyback spikes are kept within sensible limits (say 1000V-1200V
for EL84/6V6 etc., and 1500V for 6L6 type amps), then it's unlikely
that any harm will be done. It's when they go way higher than this
that the tubes, transformer or sockets can flash over causing
expensive damage to the amplifier.
In summary, lower impedances _may_ stress your power tubes and shorten
their life. Higher impedances are OK to a point, then it becomes
Russian Roullete.
>Where do wive's tales originate???
Hmmm... Mix Rock'n'Roll with beer? ;-)
>How are us guitar players supposed to
>keep everybody's stories straight?
It's unlikely you will ever keep all of the stories straight due to
all the different factors involved.
Where running high impedances are concerned, much depends on:
* Quality of output tubes
* Material used for the sockets
* Leakage inductance of the output transformer
* Quality of insulation in the output transformer
* Amount of negative feedback in the power stage
* The volume you play at
* The level of mismatch
For running low impedances, the amount of extra stress will be
influenced by:
* The class of the amplifier (A/AB)
* The volume you play at
* The level of mismatch
Given all of the variables above, it's difficult to hand out blanket
statements like X is good but Y is bad. The only totally safe advice,
is to ensure that what's stamped on the cab matches what's stamped on
the amp.
If you can't do this for practical or emergency reasons, follow LV's
advice and go low instead of high - there's a lot less to go wrong
that way...
--
Duncan Munro BOF #23
http://www.duncanamps.com
Lord Valve
The confusion arises from the fact that the two types of
guitar amplifiers (tube and the icky kind) are exactly
opposite when it comes to this particular question.
If you load a solid state amp with a lower impedance
than spec, it will try to deliver more current than the
output transistors are rated at. Unless there are good
current-limiting circuits in the output stage, this will
result in high smoke output. When loaded with a higher
impedance, the only effect is that less power is delivered
to the load. This is beneficial to the amp. Tube amps, on
the other hand, couple the output devices (tubes) to the
load through a transformer; this type of circuit can only
deliver full power to the load when seeing the correct
impedance. Higher *or* lower impedances than spec
result in inefficient power transfer. The joker in the
deck is the inductive component; when the secondary
is too lightly loaded (higher than correct impedance)
a process similar to autoforming takes place, which
causes high-voltage spikes in the primary. If of sufficient
voltage, such a spike can jump across the phenolic
(or ceramic) surface of a power tube socket and enter
the filament circuit, which is only a fraction of an ohm
above DC ground. When this happens, an arc-trail
(burn mark) is formed on the socket (or the tube, or both)
that is of relatively low resistance; arcs can then recurr
much more easily. Continued HV spikes can puncture the
insulation in the output tranny. When this happens, you'll
have to make a large contribution to the Lord Valve Home
for Lord Valve before you can rock some more. Don't do it.
Lord Valve
VISIT MY WEBSITE: http://www.freeyellow.com/members2/lord-valve/
Good tube FAQ for newbies. Click the e-mail link and join my
SPAM LIST; just put "SPAM ME" in the header and I'll sign you
up. (If you only want a set of e-mail catalogs, put "CATS ONLY"
in the header.) I specialize in top quality HAND-SELECTED NOS and
current-production vacuum tubes for guitar and bass amps. Good
prices, fast service. TONS of gear and parts in stock...let's DEAL!
NBS Electronics, 230 South Broadway, Denver, CO 80209-1510
Phone orders/tech support after 1:00 PM Denver time at 303-778-1156
NOW ACCEPTING VISA AND MASTERCARD
CHAT WITH LORD VALVE: Log onto any DALnet server and join
channel #CONELRAD. Look for me there most any night after
11:00 PM Denver (Mountain) time. Guitar-amp questions and
what-have-you are welcome.
Philo T. Farnsworth sez, "Vacuum tubes kick major ass.
Be a MAN...and buy some TODAY!"
Kent Pearson wrote:
> I'm not doubting LV at all, I know far less about it. But LV, I have to
> point out that this is not the first person who's been given this exact same
> misinformation. I've also heard the same thing from various sources for
> years now, namely that higher impedance was ok but that lower was disaster.
> Where do wive's tales originate??? How are us guitar players supposed to
> keep everybody's stories straight?
>
Lord Valve
LV
tubegod wrote:
> So you are saying if my amp is looking for 8ohms and I hook up
> an overall impedence of 4ohms, which is described as being a
> heavier load than 8ohms because the amp has to come up with more
> current,I'd be better off? Hmm, I guess I should call all the
> publishers of electronics refernce materials and give them your
> number...
>
Count Scrofula
The funniest part is the screen name. I know to follow the lord of valves,
not the god of tubes.
Lord Valve <detr...@ix.netcom.com> wrote in message
news:3970A892...@ix.netcom.com...
Robert M. Braught
>
> Lord Valve Speaketh:
>
> The confusion arises from the fact that the two types of
> guitar amplifiers (tube and the icky kind) are exactly
> opposite when it comes to this particular question.
> If you load a solid state amp with a lower impedance
> than spec, it will try to deliver more current than the
> output transistors are rated at. Unless there are good
> current-limiting circuits in the output stage, this will
> result in high smoke output. When loaded with a higher
> impedance, the only effect is that less power is delivered
> to the load. This is beneficial to the amp. Tube amps, on
> the other hand, couple the output devices (tubes) to the
> load through a transformer; this type of circuit can only
> deliver full power to the load when seeing the correct
> impedance. Higher *or* lower impedances than spec
> result in inefficient power transfer. The joker in the
> deck is the inductive component; when the secondary
> is too lightly loaded (higher than correct impedance)
> a process similar to autoforming takes place, which
> causes high-voltage spikes in the primary.
Do 'flyback' diodes do any *real* good? It occurs to me that if they do,
for a dollars worth of parts (since I'm in there anyway) I could be
potentially lengthening the life of the amp.... (and adding to the
future 'vintage amp market' stock)
-Robert
PMG
Kent Pearson wrote:
>
> On 15-Jul-2000, PMG <av...@mediaone.net> wrote:
>
> > And actually, I'd like to hear more about the history of the amps with
> > the fried sockets, tubes, capacitors, and xformers. Are we talking
> > about amps that were running at 10 for 4 & more hours a day? Are we
> > talking about amps that had extreme mismatches in the speaker
> > impedance? Are these people who were using 16 or 32 or worse ohm
> > speakers in an 4 ohm amp, or are we talking about people who used 8ohms
> > into a 4ohm amp?
>
> Exactly. I've done this many many times over the years with no apparent
> problems. Of course, it MUST happen or else we wouldn't be talking about
> it. And I certainly wouldn't recommend to anyone. It just that it's never
> happened to *me* in all these years. I guess some amps may be more
> "durable" (for lack of a better word) than others. Is it possible to fuse
> protect against the ill effects described in the quote as being possible
> from (accidental) mismatch?
>
> - KP
I generally say Lord Valve is right about things, but I don't believe in
the bullshit like the guy who keeps saying "trust in the lord". Ok, but
nobody shows examples. It's like saying that butter is bad for your
health, you should eat margarine instead, and then decades later, you
start hearing that actually, butter is healthier than margarine. Well
what the f*ck.
Can anyone come up with an example of running a 4ohm amp with 8ohm
speakers has caused it to destruct? And can you honestly say there are
no other factors? And that's one of the things I'm interested in, if
that amp fell apart from supposedly using too many ohms, what other
factors were involved. Like I mentioned, I don't see examples.
Pete
PMG
Simply Steve wrote:
>
> I can offer what little history I have...
>
> Before I bought new spkrs for my Vibrolux Reverb all I had were 4 ohm 10" spkrs,
> The VR calls for a 4 ohm load, I asked LV which was better and he told me to wire
> em up for 2 ohms, I did and gigged HEAVILY (read every weekend and then some) that
> way with the amp for almost a year. No damage. In fact I am still using the same
> tubes.
>
> I know that's not the type of history you asked for...
>
> Steve
You're right, it's not the type I was looking for. It does show that
that Fender tolerated _lower_ ohms than it asked for, but it doesn't
show that I will damage my Bassman by using one 8ohm speaker instead of
the 4ohms that it's asking for.
I was recently kicking around an idea of putting together an isolation
cabinet with 2-8ohm speakers wired for 4ohms that would have variable
leakage to adjust the volume, but I've been too lazy to sit down and
design a leakage aperture to make it work, besides, I don't feel like
building it.
Pete
>
> PMG wrote:
>
> > And actually, I'd like to hear more about the history of the amps with
> > the fried sockets, tubes, capacitors, and xformers. Are we talking
> > about amps that were running at 10 for 4 & more hours a day? Are we
> > talking about amps that had extreme mismatches in the speaker
> > impedance? Are these people who were using 16 or 32 or worse ohm
> > speakers in an 4 ohm amp, or are we talking about people who used 8ohms
> > into a 4ohm amp?
> >
> > I started looking for a way to cross check this info other than using
> > deja archives, but I need to look around some more, I'm not finding the
> > info yet.
> >
> > Pete
> >
Ken Gilbert
I go now:
The crux of the problem lies in the--as LV pointed out--the inductive
nature of the output tranny. Inductive loads are pretty special
things, since they STORE energy in a magnetic field. A property of
this effect, as has been pointed out, is that the voltage can soar to
levels _above_ the supply voltage in the amplifier--sometimes WAY
above. You can't do that with any other kind of load other than
inductive.
Now the transformer doesn't have an impedance of it's own; it only
reflects an impedance from one winding to another in proportion to the
turns (or voltage--they are the same) ratio squared.
So imagine that you've got an open secondary. This impedance is for
all intents and purposes infinite. Thus, regardless of the turns
ratio, the primary impedance is infinite as well. (leakage inductance
and parasitic capacitance--two unavoidable nasties of real-world
trannies--will limit this to some finite number less than infinity, but
suffice it to say it's damned high.) This means that the primary will
act like a constant current source, attempting to keep changes in
currents through its windings to a minimum. This will be an important
point later.
Operating into such a humungous load impedance will cause the plate to
swing HUGE voltages, according to V=IR. Especially with
tetrodes/pentodes, which are much better at cranking out current, the
delta Ip will stay the same regardless of the load. Consider what
happens when the R goes sky high.
Now, if the load were NOT inductive, the maximum possible voltage
generated would be equal to the rail voltage. No problem. This is how
it is in SS amps. But with tube amps, that's not the case.
The primary danger here is in the development of these extraordinarily
high voltages, which can punch through winding insulation, arc over
tube sockets, even arc inside the tubes themselves. Once an arc has
struck you can be pretty damned sure it will happen again. And again.
This is not good. Probably the worst scenario is that the OPT primary
arcs to the core, which is grounded, and that will cause mega current
to flow. The OPT is toast, and the power supply will be too unless
something stops that current in a fucking hurry.
So that's what can happen with too high a load. Admittedly, this is an
extreme case scenario here, where you've got an OPEN secondary, and
thus a very very high primary impedance to work into.
Notice above how i pointed out that tetrodes/pentodes will have a worse
time of this than triodes. This is because of their much higher
dynamic plate impedance, which can also be described as their being an
approximation of current sources. The pentode will just keep cranking
out plate current--regardless of what potential the plate is. The
electrostatic shielding effect of the screen grid continues to "pull"
electrons from the cathode with the same force. Thus the plate current
is largely independent of the plate voltage, a mark of high plate
impedance. That current is what "builds up" (so to speak) when working
into a high load impedance and generates the excessive voltages. It's
almost as if you've got a constant current load (the unloaded OPT) on a
constant current generator (the plate of the pentode)--obviously if
these two devices are "concerned" with currents, not giving a shit
about the voltages involved, you can get some pretty crazy effects.
With a triode, the much lower plate impedance limits the extent to
which the plate voltage will swing about uncontrolled. As the plate
swings high, for example, the attraction of electrons from cathode to
plate will increase due to the higher voltage. More electrons will be
pulled to the plate, regardless of what the control grid is doing.
More negatively charged electrons means less positive voltage, so the
voltage is "automatically" decreased. This is a direct measure of
plate impedance.
In fact, running a triode into a very high impedance is done all the
time with interstage transformers, which generally are very lightly
loaded. The inherent degeneration in the plate circuit keeps the peak
voltages from becoming a problem. Actually, triodes "love" current
loads of very high impedance--the tube is operated in its most linear
fashion and is free to do what it does best--generate an output
VOLTAGE.
You can think of the dynamic plate impedance of the tube as forming a
voltage divider, with the inductive tranny between plate and B+, and
the tube itself between plate and ground. Obviously, with the low
plate impedance of a triode, the voltage cannot swing madly about. Now
consider the very high plate impedance of a pentode, and how much
higher those plate voltages can swing.
Ok, that's the situation of too HIGH a load impedance. So what about
too LOW of an impedance? Let's consider a dead shorted secondary on
the OPT.
Now the primary presents a very low load to the tube, a low impedance,
a vertical load-line. We will notice that the tables have exactly
turned.
Since the triode's plate is like a voltage source, it will attempt to
pass incredible amounts of current in a heroic attempt to make the
plate voltage swing. Operating into a dead short, it cannot do this,
so something eventually will give. The cathode will attempt to emit
way more electrons than it can, and it will have a short, hot life.
The pentode, however, is more of a current source, so it will continue
to pass the total plate current in accordance with the screen voltage
and the control grid voltage. These have not changed with the
alteration of the load, so the pentode will continue to merrily pump
its current swings into a dead shorted load.
Take a look at some plate curves, if you need to. Find some for
pentodes and for triodes. Better yet, find some for the same power
pentode connected as a triode (g2 connected to anode).
First the pentode case: look at the way the curves lie on the page.
Imagine a horizontal load line (infinite load, open secondary) drawn on
the graph. Notice how the pentode doesn't look like it would work this
way--an infinitesimal control grid voltage change would produce a
gargantuan change in plate voltage. The tube is NOT happy. Now
imagine a vertical load line (zero load, shorted secondary). The
pentode's peak current for a given control grid voltage doesn't change
much at all--the vg1=0 plate curve is nearly horizontal for most power
pentodes, cutting right across all of the various plate voltage
points. It doesn't matter what Vp is at all--no matter where you draw
that vertical line, the peak plate current is pretty much the same.
The tube is happy.
Now the triode case: imagine the horizontal load line now. Notice how
the plate voltage is almost PERFECTLY proportional with respect to
control grid voltage. No matter which tube you try, or what current
you draw that horizontal line at, it will be VERY linear. The tube is
happy. Then consider the shorted output tranny case, with a vertical
load line. Notice how the vg1=0 curve will produce a humungous plate
current since the plate curves are so much "steeper" than the pentode's
case. The tube is NOT happy.
What the hell does all this mean? Well, hopefully you aren't running
ANY tube amp into a shorted or open load... Since no pentode is a
perfect current source, and no triode is a perfect voltage source, the
actual characteristics are somewhere between the two idealized cases.
As LV pointed out, you're much better off running a pentode amp into a
lower load impedance than it expects. For those of you with triode
output tubes, or a triode switch, you're better off running into a
HIGHER load impedance. If you don't see why by now, reread this damned
essay. It's also a good idea to take a high value power resistor, say
470R, and hard wire it right from the OPT secondary's 16R tap to
ground. This will dissipate a very small amount of power under normal
conditions, but will limit the extent to which the primary impedance
will tend towards infinity in the case of a disconnected load.
For what it's worth, I've been deliberately "mismatching" load
impedances by one tap for years. In other words, either a 4R or a 16R
load on an 8R tap, and so on. This small mismatch will limit output
power and will change the clipping points of the output tubes, but will
not damage anything in a properly designed amplifier. Keep in mind
that a higher load impedance in a pentode amp will put additional
stress on the screens, so you may want to have at least 1k stoppers
installed. A lower load impedance will cause more plate current to
flow, and if you're running the tubes at the edge of acceptable
quiescent plate dissipation that may push them over the edge into the
red zone. If you've got an old vintage amp you'd hate to see get
damaged, by all means, play it safe and don't mismatch at all. But if
you're wondering about how it sounds, and the amp's got good trannies
in it, then mismatch away. Just keep it within ONE TAP please, for
safety's sake.
Ken Gilbert
--
I know that the twelve notes in each octave and the varieties
of rhythm offer me opportunities that all of human genius
will never exhaust. --Igor Stravinski
Sent via Deja.com http://www.deja.com/
Before you buy.
Danny Russell
"Nick V. Flor" wrote:
>
> Thanks everyone. I'm the original poster. Just a little more history...
> the reason I was asking is that I recently finished building a tube amp kit
> (Torres Tiny Tone, 2-12ax7s, 1-6005, 1.5W Amp), and I had the option of
> wiring it up for 4, 8 or 16 ohms. I have a Tone Master 2x12 cab with
> Vintage 30s in it, and that's 16 ohms.
In three weeks this whole thread will start over from scratch like
it never happened. Load mismatching is a lot like that shallow pond
with the sign around it that says: "WARNING - SHALLOW WATER - NO
DIVING". Christ, you could have people sitting in wheelchairs all
around the perimeter with neck braces on shouting warnings, and
nebies would walk up and dive right in.
> However, it seems like most cabs are 8ohms, so I just wired it up for 8
> ohms. I asked AGA my question cuz I wanted to know if I was damaging my amp
> by hooking it up to the ToneMaster cab.
Funny you should mention the ToneMaster. Actually I think the
ToneMaster is a big part of this whole misunderstanding. The manual
encourages experimenting with load mismatches to allow more sonic
variations. -Danny
--
<<<GET BLITZED!!!>>>
http://home.flash.net/~blitz/tunes.html
To get inside my whacky head.
Tom
recommendation of Willie's past advice, and not intended to be bullshit.
Perhaps a better suggestion is that for maximum efficiency and full use
of your rig, give the amp the impedance it expects. For my part, I
don't intend to ever intentionally mis-match the impedence. Why take a
chance with expensive tools?
Regards.
PMG wrote:
>
> Kent Pearson wrote:
> >
> > On 15-Jul-2000, PMG <av...@mediaone.net> wrote:
> >
> > > And actually, I'd like to hear more about the history of the amps with
> > > the fried sockets, tubes, capacitors, and xformers. Are we talking
> > > about amps that were running at 10 for 4 & more hours a day? Are we
> > > talking about amps that had extreme mismatches in the speaker
> > > impedance? Are these people who were using 16 or 32 or worse ohm
> > > speakers in an 4 ohm amp, or are we talking about people who used 8ohms
> > > into a 4ohm amp?
> >
> > Exactly. I've done this many many times over the years with no apparent
> > problems. Of course, it MUST happen or else we wouldn't be talking about
> > it. And I certainly wouldn't recommend to anyone. It just that it's never
> > happened to *me* in all these years. I guess some amps may be more
> > "durable" (for lack of a better word) than others. Is it possible to fuse
> > protect against the ill effects described in the quote as being possible
> > from (accidental) mismatch?
> >
> > - KP
>
> I generally say Lord Valve is right about things, but I don't believe in
> the bullshit like the guy who keeps saying "trust in the lord". Ok, but
> nobody shows examples. It's like saying that butter is bad for your
> health, you should eat margarine instead, and then decades later, you
> start hearing that actually, butter is healthier than margarine. Well
> what the f*ck.
>
> Can anyone come up with an example of running a 4ohm amp with 8ohm
> speakers has caused it to destruct? And can you honestly say there are
> no other factors? And that's one of the things I'm interested in, if
> that amp fell apart from supposedly using too many ohms, what other
> factors were involved. Like I mentioned, I don't see examples.
>
> Pete
Tom
Thanks, Ken.
PMG
for me to digest actually though. I'll re-read it.
A question, When you say:
"But if you're wondering about how it sounds, and the amp's got good
trannies
in it, then mismatch away. Just keep it within ONE TAP please, for
safety's sake." Ok, "ONE TAP", are you referring to transformer taps
for speaker ohms? And are they generally 4 ohms apart, and would that
make running my Bassman at 8 ohms ok? Because, a couple things, 1) yes
it is a new xformer, and 2) since I use an Altair, I think it always
provides an 8ohm load regardless of the speakers plugged into it. I
went looking for the instruction book that came with it when LV said I
was full of shit about this, but the book is still lost, my memory tells
me that it's always 8ohms though.
Pete
--
PMG
Duncan Munro wrote:
>
> On Fri, 14 Jul 2000 11:21:41 GMT, "Kent Pearson"
> <Delt...@Xma.freei.netX> wrote:
>
> >I'm not doubting LV at all, I know far less about it. But LV, I have to
> >point out that this is not the first person who's been given this exact same
> >misinformation. I've also heard the same thing from various sources for
> >years now, namely that higher impedance was ok but that lower was disaster.
>
> Kent, it's not quite as easy as that :-(
>
> * Lower impedance will _generally_ stress the power tubes gradually
> more and more as the volume goes up.
>
> * Higher impedance will _generally_ stress the power tubes less as the
> volume goes up until the powertubes cut off at high volume levels.
> This will create voltage spikes on the plates of the power tubes
> called flyback.
Ok, for someone like me, who onlt knows enough to be dangerous, this
isn't clear what you're saying. Specifically "until the powertubes cut
off". What are you talking about when you say "cut off"? Is this
referring to a power interuption? Are you talking about something that
happens when the amp is driven extremly hard? Or is this an interuption
in the connection to the speaker? Or did I completly miss on all those
guesses?
Pete
>
> If the flyback spikes are kept within sensible limits (say 1000V-1200V
> for EL84/6V6 etc., and 1500V for 6L6 type amps), then it's unlikely
> that any harm will be done. It's when they go way higher than this
> that the tubes, transformer or sockets can flash over causing
> expensive damage to the amplifier.
>
> In summary, lower impedances _may_ stress your power tubes and shorten
> their life. Higher impedances are OK to a point, then it becomes
> Russian Roullete.
>
> >Where do wive's tales originate???
>
> Hmmm... Mix Rock'n'Roll with beer? ;-)
>
> >How are us guitar players supposed to
> >keep everybody's stories straight?
>
--
Count Scrofula
This sort of mismatch will work. For a while. At reduced volumes, no sweat
for sometime, just not optimum efficiency or frequency response.
Best bet: Match the loads correctly, particularly for long life and best
sound.
In this case, the original poster had just done up a Torres Tinytone -- not
exactly cheap. Sure, he can test it on the mismatched cab, but it makes no
sense to cut corners at this juncture...and I would wonder, if you've gone
to the trouble of the Torres, which most people would use to get cranked
tone at relatively low volumes [albeit far too loud for the delicate ears of
cybermonk] why would you be feeding it into a relatively loud cab?
PMG <av...@mediaone.net> wrote in message
news:3970EA45...@mediaone.net...
tubegod
reasoning. Thats all I was interested in. I admit my electronics
training started with Solid State and went into digital, it
didn't touch tube stuff. However, since I was only repeating
what I've been told since Day One in "Not tube theory 101", I
don't think I was owed any flames. I hope you aren't still
pissed about the scoff you and Rocafforte had.... I read just
about every thread that you post on and learn as much as I can.
I was pissed because your website is not as near as informative
as your posts here. Of course you probably have nothing but time
to update it... <grin>
Bryan
tubegod
>Some of us only open our yaps when we are pretty sure we have a
clue.
>
>The funniest part is the screen name. I know to follow the
lord of valves,
>not the god of tubes.
>
>Lord Valve <detr...@ix.netcom.com> wrote in message
>news:3970A892...@ix.netcom.com...
>> <sigh> Newbies...
My screen name has nothing more to do with how much I know as it
does the fact that its the first thing that popped into my head.
PMG
Stefan Markowitz wrote:
>
> PMG schrieb in Nachricht <3970E6FB...@mediaone.net>...
> <---snip--->
>
> >And are they generally 4 ohms apart, and would that
> >make running my Bassman at 8 ohms ok? Because, a couple things, 1) yes
> >it is a new xformer, and 2) since I use an Altair, I think it always
> >provides an 8ohm load regardless of the speakers plugged into it. I
> >went looking for the instruction book that came with it when LV said I
> >was full of shit about this, but the book is still lost, my memory tells
> >me that it's always 8ohms though.
>
> 1) How did you blow the original xformer?
Good question! It was messed up when I got the amp. The tech tells me
that the wire that normally goes to the heater was fried out an cut off,
and that the person had just connected the heater to one of the other
wires. This amp had never been in good shape (while I've owned it)
until about a month ago. I've never used it all that much because I
knew it needed work, I just knew it had a great sound, so I hung on to
it.
>
> 2) This is not possible. The Altair does not know which load you have
> connected, so it isnæ„’ able to provide a 8Ohm load to the amp regardless
> of your speaker. This would presuppose a sophisticated circuit which
> would sense the speaker impedance and set the attenuation network
> to the required values - which it doesnæ„’.
Well, there's nothing the least bit sophisticated going on in an
Altair. It appears to be a toaster coil to me. So are you saying, that
if I hook 2 speakers as 4 ohms to the Altair, that the amp will also get
4 ohms? And that would solve this whole impedance question for me?
That would be convenient.
Pete
>
> BTW: I扉e never experienced any problems by impedance mismatching
> ("one tap" or even "two taps"). But I donæ„’ recommend this to anybody
> who does not know what heæ„€ doing. "Donæ„’ try this at home" :-)
>
> I悲 be carefull with high power amps (above 50W). My JCM900 50W
> is unimpressed by mismatched speaker load (despite of its "puny"
> -haha- ouput tranny), same goes for my Echolette (4* EL84) from the
> 60ies which is still alive. I have an old Siemens amp which I moded for
> guitar use (2*EL34). It runs at 650V B+ ! I rewinded (rewound?) the
> output tranny because it only had a 100V tap. I calculated the number
> of turns by the famous formula "Pi times diameter of thumb" so you
> can be sure that there is a gross impedance mismatch.
> I played that amp for years with different cabs, never had any problems
> except for a broken bias pot which caused the tubes to glow bright red.
> Even this did not impress the tubes (Siemens EL34). I扉e never changed
> them. They are better than new ones.
> I悲 like to add that I played those amps at their limits, fully cranked (why
> tubes if you don愒 crank 悶m?)
>
> Stefan
Robert M. Braught
>
> Kent Pearson wrote:
> >
> > On 15-Jul-2000, PMG <av...@mediaone.net> wrote:
> >
> > > And actually, I'd like to hear more about the history of the amps with
> > > the fried sockets, tubes, capacitors, and xformers. Are we talking
> > > about amps that were running at 10 for 4 & more hours a day? Are we
> > > talking about amps that had extreme mismatches in the speaker
> > > impedance? Are these people who were using 16 or 32 or worse ohm
> > > speakers in an 4 ohm amp, or are we talking about people who used 8ohms
> > > into a 4ohm amp?
> >
> > Exactly. I've done this many many times over the years with no apparent
> > problems. Of course, it MUST happen or else we wouldn't be talking about
> > it. And I certainly wouldn't recommend to anyone. It just that it's never
> > happened to *me* in all these years. I guess some amps may be more
> > "durable" (for lack of a better word) than others. Is it possible to fuse
> > protect against the ill effects described in the quote as being possible
> > from (accidental) mismatch?
> >
> > - KP
>
> I generally say Lord Valve is right about things, but I don't believe in
> the bullshit like the guy who keeps saying "trust in the lord". Ok, but
> nobody shows examples.
Ok, for example, has anybody had (and confirmed the cause of) the
Marshall JCM900 (i.e. 2500SL-X) rear panel 'board fry' failure?
Unfortunately I only end up seeing amps after they're already hurt, and
when I ask 'how did it happen', I usually only get a nod and a ? stare.
What I see periodically is one of these where the output transformer
screen tap connections have arced/shorted at the high/low switch (burnt
rear panel jacks/switches circuit board); I've always figured this was
due to mismatch at high volume (I hold Marshall liable for the great job
of labeling the two position impedance switch: (4)16 or 8 ; I figure a
user might innocently put a 4 ohm load on the 16 ohm position?)
FWIW I've never had to replace an output tranny on one of these; just
remove enough carbonized pc board around the area, a little hard wiring,
and they stay good.
-Robert
Count Scrofula
impedance from there" thread...
Dave <vampy...@aol.comFUspam> wrote in message
news:20000715213215...@ng-fl1.aol.com...
> Related Question...what about a cab where you DON'T KNOW the ohmage? sure
you
> can guess, but what about using more than one cab in that situation? Thats
like
> inviting disaster so, I aint doing it...YES, you can open the cab up...but
I've
> seen ones where there are NO markings on the speaker or cab telling me
> ohmage/wattage info...what then?
>
> Some of my personal stuff this concerns includes...
>
> 2x12 cab w/Fane speakers (I think theyre 16ohm each, cant really
tell...cab is
> wired for 8 total)
>
> Dean Markley 4x12 (yeah it suxx I know)...DM speakers, I could open it up,
the
> ohm values are on the speakers...I'm mostly concerned with how the cab is
wired
> up...
>
> '72 Fender Twin (SF)...both speakers stock, have no info on them ...ext
cab
> jack sez something like 100 watts 4 ohms total...without knowing the ohm
value
> of the built in speakers, this info is no help, correct?
>
> Thanx 4 help
> Dave
> +;-E
Count Scrofula
Perhaps you should try "tubenumbnuts"
than everyone will have a good idea how much stock to put in your
misinformation.
Oh yeah, you can bet that LV does not still have a hard on after the little
rocketfart imbroglio.
tubegod <tubegod...@hotmail.com.invalid> wrote in message
news:1ed19877...@usw-ex0106-046.remarq.com...
PMG
PMG wrote:
>
> Stefan Markowitz wrote:
> >
> > PMG schrieb in Nachricht <3970E6FB...@mediaone.net>...
> > <---snip--->
> >
> > >And are they generally 4 ohms apart, and would that
> > >make running my Bassman at 8 ohms ok? Because, a couple things, 1) yes
> > >it is a new xformer, and 2) since I use an Altair, I think it always
> > >provides an 8ohm load regardless of the speakers plugged into it. I
> > >went looking for the instruction book that came with it when LV said I
> > >was full of shit about this, but the book is still lost, my memory tells
> > >me that it's always 8ohms though.
> >
> > 1) How did you blow the original xformer?
>
> Good question! It was messed up when I got the amp. The tech tells me
> that the wire that normally goes to the heater was fried out an cut off,
> and that the person had just connected the heater to one of the other
> wires. This amp had never been in good shape (while I've owned it)
> until about a month ago. I've never used it all that much because I
> knew it needed work, I just knew it had a great sound, so I hung on to
> it.
>
> >
> > 2) This is not possible. The Altair does not know which load you have
> > connected, so it isn´t able to provide a 8Ohm load to the amp regardless
> > of your speaker. This would presuppose a sophisticated circuit which
> > would sense the speaker impedance and set the attenuation network
> > to the required values - which it doesn´t.
>
> Well, there's nothing the least bit sophisticated going on in an
> Altair. It appears to be a toaster coil to me. So are you saying, that
> if I hook 2 speakers as 4 ohms to the Altair, that the amp will also get
> 4 ohms? And that would solve this whole impedance question for me?
> That would be convenient.
>
> Pete
>
About this question. I found the Altair Manual, and if I give the
Altair 4ohms of speakers, then the amp will see 3.9 to 8ohms, the way
I've been using it, with an 8ohm of speaker, the amp would see 5 to
8ohms. So I'll solve _my_ problem by putting together another cord
(where do I keep loosing them to?) and hook in another speaker so the
amp will see a more friendly ohms load. Thanks everyone for the help.
While I was digging for the Altair Manual, I found the receipt for the
Bassman, and I got it for a better deal than I had remember. I got it
for $135 in 1982, much better than what I was thinking, I thought I had
paid $225, but that was for the Princeton Reverb. So I was sitting on
this amp that was in trashy condition for a long time, but at least I
didn't pay as much for it as I thought I did! WooHooo.
Pete
Lord Valve
Lord Valve Speaketh:
I used to put 'em in whenever an amp came in with fried
sockets. For the last ten years or so, I haven't been
using them much; I'd rather concentrate on curing the
cause rather than treating the symptoms. Nowadays,
if it's a head, I make the owner bring his whole rig
in so I can go completely through the *entire* output
circuit...the part inside the amp, which includes
the power stage, the impedance selector switch (if any)
and its associated wiring, the output jack and wiring;
and the part *outside* the amp, which includes the
speaker wire, the cabinet jack(s), the internal cabinet
wiring, and the speakers themselves. I also make sure
that the owner gives me a complete report on what he
was doing with the amp when it failed. (You'd be surprised
at how often I hear that the amp was accidentally played
without the speaker plugged in.) I also give 'em my
lecture on proper setting of the impedance selector switch,
and I try to instill some healthy paranoia on the subject
of making *SURE* the speaker cable is plugged into the
cabinet *and* the head...I tell 'em if it isn't, they just spent
$100 with the first note they play. For total space-cases,
I put the clamp diodes in, yes...but those guys always
make me nervous; when the clamps blow, they blow the fuses
in the amp. They'll keep blowing fuses until they're
replaced...and you know what musicians do when they run
outta fuses. (Gotta write a letter of appreciation to
the Reynolds Wrap folks...their product paid for my
house. ;-) So Sayeth the Lord.
Lord Valve
VISIT MY WEBSITE: http://www.freeyellow.com/members2/lord-valve/
Good tube FAQ for newbies. Click the e-mail link and join my
SPAM LIST; just put "SPAM ME" in the header and I'll sign you
up. (If you only want a set of e-mail catalogs, put "CATS ONLY"
in the header.) I specialize in top quality HAND-SELECTED NOS and
current-production vacuum tubes for guitar and bass amps. Good
prices, fast service. TONS of gear and parts in stock...let's DEAL!
NBS Electronics, 230 South Broadway, Denver, CO 80209-1510
Phone orders/tech support after 1:00 PM Denver time at 303-778-1156
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CHAT WITH LORD VALVE: Log onto any DALnet server and join
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11:00 PM Denver (Mountain) time. Guitar-amp questions and
what-have-you are welcome.
"I got the chop...I'll never get popped." - Tower of Power
Stefan Markowitz
>And are they generally 4 ohms apart, and would that
>make running my Bassman at 8 ohms ok? Because, a couple things, 1) yes
>it is a new xformer, and 2) since I use an Altair, I think it always
>provides an 8ohm load regardless of the speakers plugged into it. I
>went looking for the instruction book that came with it when LV said I
>was full of shit about this, but the book is still lost, my memory tells
>me that it's always 8ohms though.
1) How did you blow the original xformer?
2) This is not possible. The Altair does not know which load you have
connected, so it isnæ„’ able to provide a 8Ohm load to the amp regardless
of your speaker. This would presuppose a sophisticated circuit which
would sense the speaker impedance and set the attenuation network
to the required values - which it doesnæ„’.
Nick V. Flor
through -- what's supposed to be -- a good cab, which I had lying around the
house.
Surprisingly none of the local stores stock a 1x12 cab -- lots of 4x12s. I
have to order one so in the mean time I need something to play it through.
- Nick
"Count Scrofula" <bre...@airxmail.next> wrote in message
news:00CBDCB5D82EE070.79E72A35...@lp.airnews.net...
Duncan Munro
>Ok, for someone like me, who onlt knows enough to be dangerous, this
>isn't clear what you're saying. Specifically "until the powertubes cut
>off". What are you talking about when you say "cut off"? Is this
>referring to a power interuption? Are you talking about something that
>happens when the amp is driven extremly hard? Or is this an interuption
>in the connection to the speaker? Or did I completly miss on all those
>guesses?
When I say "cut off", I mean that one of the power tubes (assuming
push pull) is not drawing current. This leaves the tube in a high
impedance state with current still flowing through the leakeage
inductance in the output tranny on the side of the transformer
connected to that tube.
It's nothing to do with killing the mains power, or problems with the
speaker connection.
Dave
Bob
Hey Lord - I know this is a REAL boring thread for you - but in your
experiance, have you seen damage from a small mismatch like 16 not 8,
or even 8 not 4? And if you were real paranoid, what value resistor
would you put across the output just in case the player shreds the
speaker for real?!?!?
Just Curious Bob
>On Sat, 15 Jul 2000 12:08:18 -0600, Lord Valve <detr...@ix.netcom.com> wrote:
><sigh> Newbies...
>LV
>
>tubegod wrote:
>
>> So you are saying if my amp is looking for 8ohms and I hook up
>> an overall impedence of 4ohms, which is described as being a
>> heavier load than 8ohms because the amp has to come up with more
>> current,I'd be better off? Hmm, I guess I should call all the
>> publishers of electronics refernce materials and give them your
>> number...
>>
Danny Russell
Stefan Markowitz wrote:
>
SNIP
> 2) This is not possible. The Altair does not know which load you have
> connected, so it isn´t able to provide a 8Ohm load to the amp regardless
> of your speaker. This would presuppose a sophisticated circuit which
> would sense the speaker impedance and set the attenuation network
> to the required values - which it doesn´t.
SNIP
Actually, by the time you've attenuated to the second click and
everything below that, the Altair is showing an 8 ohm load to the
amp. On the first attenuation click the reflected impedance is
about halfway between 8, and whatever the cabinet is. -Danny
Lord Valve
Bob wrote:
> Hey Lord - I know this is a REAL boring thread for you - but in your
> experiance, have you seen damage from a small mismatch like 16 not 8,
> or even 8 not 4? And if you were real paranoid, what value resistor
> would you put across the output just in case the player shreds the
> speaker for real?!?!?
Sure, I've seen it. Hell, I've been fixing amps
for 38 years (nearly 30 professionally) and I've
seen every failure mode there is. (Probably.
Until a couple of days ago, I never saw anyone
get zapped with B+ off a non-electrodynamic
speaker's frame...) You're more likely to have
an arced socket when loading a 4-ohm tap with 8
(or an 8 with 16) if the amp is being played at
full throttle with a really trebly tone than you
are if it's a jazz player with a fat hollowbody
using a bassy tone at low volume during a cocktail
gig. Loading a 4-ohm amp with 16 is *always*
a crapshoot, especially if you play loud. You're
more likely to get away with it when you're running
a closer mismatch; like Ken said, the amp's design
has a lot to do with this, too. I use a Dynaco
MK III as my bench amp, and I've done shit to it
that would destroy a Marshall. In 25 years, it's
never so much as blinked. For a failsafe, I'd put
a 250 ohm resistor across the output.
LV
Lord Valve
since the guys who didn't believe me or Duncan probably
don't have the technical mojo to understand your post
anyway, but this is still a really great post. Eespecially
the pentode/triode load line stuff...I was more concerned
with the magnetic end of things, but that's good reading.
This will probably be one of the two or three I save each year. ;-)
LV
Ken Gilbert wrote:
(good shit)
Rich Koerner
PMG wrote:
>
> Kent Pearson wrote:
> >
> > On 15-Jul-2000, PMG <av...@mediaone.net> wrote:
> >
> > > And actually, I'd like to hear more about the history of the amps with
> > > the fried sockets, tubes, capacitors, and xformers. Are we talking
> > > about amps that were running at 10 for 4 & more hours a day? Are we
> > > talking about amps that had extreme mismatches in the speaker
> > > impedance? Are these people who were using 16 or 32 or worse ohm
> > > speakers in an 4 ohm amp, or are we talking about people who used 8ohms
> > > into a 4ohm amp?
> >
> > Exactly. I've done this many many times over the years with no apparent
> > problems. Of course, it MUST happen or else we wouldn't be talking about
> > it. And I certainly wouldn't recommend to anyone. It just that it's never
> > happened to *me* in all these years. I guess some amps may be more
> > "durable" (for lack of a better word) than others. Is it possible to fuse
> > protect against the ill effects described in the quote as being possible
> > from (accidental) mismatch?
> >
> > - KP
>
> I generally say Lord Valve is right about things, but I don't believe in
> the bullshit like the guy who keeps saying "trust in the lord". Ok, but
> nobody shows examples. It's like saying that butter is bad for your
> health, you should eat margarine instead, and then decades later, you
> start hearing that actually, butter is healthier than margarine. Well
> what the f*ck.
>
> Can anyone come up with an example of running a 4ohm amp with 8ohm
> speakers has caused it to destruct? And can you honestly say there are
> no other factors? And that's one of the things I'm interested in, if
> that amp fell apart from supposedly using too many ohms, what other
> factors were involved. Like I mentioned, I don't see examples.
>
> Pete
Ok, tell ya all what I'm going to do.
It seems that I have to put up the "Proof Page!"
Now, I know of a 400-PS that may have smoked sockets in it. When it
comes in the shop, you can bet your sweet bippy, there are going to be a
lot of pictures on That Page!!!.
Now, the most common thing is smoking up these sockets is higher than 4
ohm loads appearing on the secondary winding of the 400's output.
Even a proper load with a bad connection, or faulty wire will do the
same thing.
In the 400-PS, the socket is smoked the instant the load changed. You
don't have to wait very long. Nor, do you have to have anything plugged
into the input at the time.
Now this is a 400-PS I'm talking about here. It's not you run of the
mill amp.
However, There are some amps with over kill headroom in the designs and
selected components where you can get away with this type of mismatch
for just so long. But the RISK for amp failure is still present!!!
If you have to mismatch your load, go for the low, rather than the
higher. A tube amp
will more happy that way if it is a MUST DO THING!!!!!
But remember, the RISK Remains!!!!
Save up and put the cash in a shoe box for the day it blows. OT's,
Tubes, sockets, and resistors need replacing if you are lucky. If you
are not, add some wire, PT, and may be a speaker replacement up against
the cost of labor for the repairs.
Hmmmmmm........????????
<Thinking>
You know, I think I going to get out of character and say it how it
is!!!!
Hmmmmm.......??????
<Thinking>
When the 400-PS walks into the shop, and I open up the amp I'll see
things that REALLY Tick Me OFF!!!!! Example, smoked sockets.
User Error is more the problem cause than anything to do with the amp
alone.
Now recently there was a fellow who freaked out on me in one of the
threads on scraping the carbon off a porcelain tube socket, among other
things!!!!!!!
Idiot!!!!!!!!!
Just the kind of person you don't want in a 100 yards of a 400-PS.
He had a Marshall with 570 VDC, or some figure like that, and he's
sweating it!!
If that had been a 400-PS, my God that disaster he'd have on that bench.
They can, and will melt tubes. In the extreme, possibly flame up
components too.
Hmmmmmmm......???????
Proof?????????
<thinking>
Here, take a look!!!! http://www.timeelect.com/6550a-ex.htm
Now, that is the kind of individual that would bad mouth the 400-PS
seven ways to Sunday, never admit they were in way over their heads, and
didn't have a Clue What The Hell They Were Doing IN THAT AMP In The
First Place!!!!!!!
A few times one of my customers have been on the road and find
themselves needing repairs. So if that ever happens, and they feel
shaky about the tech, I tell them to call me from that shop.
I can't tell you how many times I've told them to RUN, not walk out of a
shop.
Once, I had to explain to a so-called amp tech that there was no reason
to pull four new GE-6550's from the Marshall that he had just put
EL-34's in that would not run.
I told him the GE's were not the problem and to put them back in the
Marshall. He then said I was full of Shit!!!!
Well, I told him when the plates get red, to call me back and I'd
explain the facts of live to him. I hung up on him.
Three hours later, my phone rang and the GE's were back in.
OK, what do I do first, was the first words out of his mouth.
He had no clue I had modified it to run harder than EL-34's could take,
the GE's were fine, and the problem was else where. Which was the way
this case turned out.
It was a bad PI tube causing the low output and the funky looking wave
shape!!
I don't remember his name, but what I can't forget about him, is the way
hey kept saying to me over the phone every time I told him a test to
make was, "I don't work this way!!!"
RIGHT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Hmmmmmmmmmmmmmmmm.........??????????
I really don't think he learned anything from the experience.
<Thinking>
Looking back at this event, I can't help but wonder what Books he had
read on the subject. The ones found in the music stores on amp repair,
or the educational vacuum tube theory ones found in the engineering
library!!!!!!!!!!!
You ALL Tell Me!!!!!!!!!!!!!!!!!!!!!!!?
<Thinking>
Of these who learned there skills from these books, which are the two
kinds of Tech are you going to take advice from!!!!!!!?
Hmmmmmmmm.........????????
Just which of these two kinds of tech do you want working on your
amp!!!!!!!!???????
Let me guess.
Regards,
Rich Koerner,
Time Electronics.
http://www.timeelect.com
Service * Repair * Modifications * Design Engineering
Live Sound & Studio Production
Bastian
wired for 12 ohm (2 speakers are 8 ohm and the other two are 16
ohm). My amp (Mesa/Boogie DC-5) has a 4 and 8 ohm out. So I use
the 8 ohm out. Actually Mesa/Boogie says you can mismatch
impedances in the manual to this particular amp. It won't be
damaged.
Anyway,my question is how much output/headroom do I lose ? What
would be the difference between the 4 and 8 ohm out ? Could I use
a Y-cable or something to connect the cab to both the 4 and 8 ohm
out - would that make it a 12 ohm out at all ? Would I sacrifice
headroom by using some Y-cable ?
Thanks for any help !
Bastian,Germany
Robert M. Braught
>
> > Robert M. Braught wrote:
> > Do 'flyback' diodes do any *real* good?
>
> I used to put 'em in whenever an amp came in with fried
> sockets. For the last ten years or so, I haven't been
> using them much; I'd rather concentrate on curing the
> cause rather than treating the symptoms. Nowadays,
> if it's a head, I make the owner bring his whole rig
> in so I can go completely through the *entire* output
> circuit...the part inside the amp, which includes
> the power stage, the impedance selector switch (if any)
> and its associated wiring, the output jack and wiring;
> and the part *outside* the amp, which includes the
> speaker wire, the cabinet jack(s), the internal cabinet
> wiring, and the speakers themselves. I also make sure
> that the owner gives me a complete report on what he
> was doing with the amp when it failed. (You'd be surprised
> at how often I hear that the amp was accidentally played
> without the speaker plugged in.)
No, unfortunately I'm not surprised, based on the fact that when
someone's in here with their whole rig (at my request, to 'check out the
whole thing', kinda like you've said), I see it happen.
> I also give 'em my
> lecture on proper setting of the impedance selector switch,
> and I try to instill some healthy paranoia on the subject
> of making *SURE* the speaker cable is plugged into the
> cabinet *and* the head...I tell 'em if it isn't, they just spent
> $100 with the first note they play. For total space-cases,
> I put the clamp diodes in, yes...but those guys always
> make me nervous; when the clamps blow, they blow the fuses
> in the amp. They'll keep blowing fuses until they're
> replaced...and you know what musicians do when they run
> outta fuses. (Gotta write a letter of appreciation to
> the Reynolds Wrap folks...their product paid for my
> house. ;-) So Sayeth the Lord.
For those *undesired* repeat scenarios, I've been known to (without
informing the customer) install the 'internal idiot fuse' ala Crown
DC-300 / Ampeg V-4B.
I guess as a (I'd like to think I am, supposedly,) informed service
person who periodically deals with *drivers with no mechanical skills*,
we can only do so much to protect someone from their own folly.
Thanks for the reply, LV
*To Serve and Protect*
-Robert
Stefan Markowitz
Lord Valve schrieb in Nachricht <397153A2...@ix.netcom.com>...
<---snip--->
>
>For a failsafe, I'd put
>a 250 ohm resistor across the output.
What about a triac (with small resistor in series) across
the output, which will be triggered through a voltage divider
if the output voltage exceeds its safe zone?
I think this would be a very good protection circuit, though
I扉e never tried it. It just came to my mind while reading
this thread.
Stefan
Danny Russell
PMG wrote:
>
> About this question. I found the Altair Manual, and if I give the
> Altair 4ohms of speakers, then the amp will see 3.9 to 8ohms, the way
> I've been using it, with an 8ohm of speaker, the amp would see 5 to
> 8ohms. So I'll solve _my_ problem by putting together another cord
> (where do I keep loosing them to?) and hook in another speaker so the
> amp will see a more friendly ohms load. Thanks everyone for the help.
>
> While I was digging for the Altair Manual, I found the receipt for the
> Bassman, and I got it for a better deal than I had remember. I got it
> for $135 in 1982, much better than what I was thinking, I thought I had
> paid $225, but that was for the Princeton Reverb. So I was sitting on
> this amp that was in trashy condition for a long time, but at least I
> didn't pay as much for it as I thought I did! WooHooo.
After I posted, I rigged up my trusty Altair to make some
measurements (again), and you are correct sir. By the third
attenuation click (-12dB), the influence of the speaker over load
conditions is practically non-existent (to the amp), and the amp
primarily sees the Altair's 8 ohm resistive load. At the second
click (-8dB), the speakers influence is slightly more measurable but
still negligible. It's the first click (-4dB) that's the real
stinker. In essence, it appears to be 8 ohms resistive in parallel
with the speaker load, so it's always going to be something less
than eight. In practical terms, it appears to show a 4 ohm load to
the amp at that setting. -Danny
PMG
I think Tiny Tubes provided a link to that page once, it seems to me
I've seen that before. Prety cool, it melted right through the wall of
the tube.
>
> Now, I know of a 400-PS that may have smoked sockets in it. When it
> comes in the shop, you can bet your sweet bippy, there are going to be a
> lot of pictures on That Page!!!.
>
> Now, the most common thing is smoking up these sockets is higher than 4
> ohm loads appearing on the secondary winding of the 400's output.
>
> Even a proper load with a bad connection, or faulty wire will do the
> same thing.
>
> In the 400-PS, the socket is smoked the instant the load changed. You
> don't have to wait very long. Nor, do you have to have anything plugged
> into the input at the time.
>
> Now this is a 400-PS I'm talking about here. It's not you run of the
> mill amp.
How many of those 400-PS amps actually exist? I never heard of the
thing until TT started talking about maybe selling one.
Thanks Rich, I saved this to a text file. Ken's was ohms.txt and this
one is ohms2.txt.
RonSonic
wrote:
>Awright, pete, since LV's and duncan's reply wasn't wordy enough, here
>I go now:
>
>The crux of the problem lies in the--as LV pointed out--the inductive
>nature of the output tranny. Inductive loads are pretty special
>things, since they STORE energy in a magnetic field. A property of
>this effect, as has been pointed out, is that the voltage can soar to
>levels _above_ the supply voltage in the amplifier--sometimes WAY
>above. You can't do that with any other kind of load other than
>inductive.
Ken! This was superb.
Thanks,
Ron
RonSonic
<S.Mar...@dontspam.gmx.de> wrote:
>If you are in doubt about LV“s statement, why don“t you just try it?
>Crank up your tube amp without a speaker connected. If you were
>right, the amp would not be damaged. (No load, no current, why
>should it be damaged? :-) )
>Hmm, when I think about, if I do that with my Dynacord Reference amp,
>nothing happens.
>Guess what: the speaker out connector shorts the output when there is no
>cable plugged in in order to protect the amp. Do you think the engineer
>who designed this was an idiot?
>Remember, we are talkin“bout tube amps, not solid state!
Let's also note that the negative feedback loop was designed to run
loaded. Unload the sensor end and some amps will take off in the most
lurid oscillations you can imagine. Also a bad thing.
Ron
RonSonic
<guitar...@worldnet.att.net> wrote:
>Thanks everyone. I'm the original poster. Just a little more history...
>the reason I was asking is that I recently finished building a tube amp kit
>(Torres Tiny Tone, 2-12ax7s, 1-6005, 1.5W Amp), and I had the option of
>wiring it up for 4, 8 or 16 ohms. I have a Tone Master 2x12 cab with
>Vintage 30s in it, and that's 16 ohms.
Correct me if I'm mistaken, that little amps has no negative feedback
and a triode output tube. If both those statements are true, then it
should be very tolerant of impedance mismatches, feel free to use
whichever impedance setting sounds best.
Ron
Rich Koerner
This is a dry run for a "form letter" type response. Just trying to
save my fingers some extra typing. The cost of rented fingers is going
up every day.
In this situation, the way I see it, there is one of three choices
available.
1. Find an educated and experienced person in such matters for the
resolve.
2. Become the educated and experienced person in such matters by way of
the proper methods of self-improvement.
3. Stay here in AGA doing what everyone else does looking for answers
for the taking.
Now, it is with number three that the outcome is unpredictable, and
sometimes subject to a means of decision making where the roll of the
dice, or flip of the coin may be of the greatest aid and assistance as a
comment/opinion filter.
In which case, I find choices 1 and 2 to be the better options.
However, these will require some manner investment.
RonSonic
Plug a cord into the cab, disconnect the amp. Stick a multimeter set
to Ohms on the cord, if it says
about 1-1.5, then call it a 2 Ohm cab
Around 3 it's a 4Ohm article
Something just over 5, we have a nominal 8 Ohm cab
You see 11, then we declare it to be a 16Ohm box.
This is all close enough to work long and well.
The other side of this coin is the guy who called me concerned that
since his Celestions are 15ohms he might have a problem.
Ron
Stefan Markowitz
RonSonic schrieb in Nachricht ...
>
>Let's also note that the negative feedback loop was designed to run
>loaded. Unload the sensor end and some amps will take off in the most
>lurid oscillations you can imagine. Also a bad thing.
You are right, but it seems to me that you are talking about some kind
of hi-fi amp with separate feedback sensing cabling.
The Dynacord Reference amp which I mentioned is a guitar amp with
an almost "normal" 2* EL34 output stage, though there is a special
feature: It has a pot in the feedback loop which allows adjustment of
the amount of negative feedback.
Stefan
Ken Gilbert
duff and actually put something from my head down on the page.
it's even better when it's somewhat coherent. i hope somebody,
somewhere gets something out of it. judging by the responses,
i'd say that happened, which is nice. it's the kind of thing
that makes me actually want to post more of the good stuff!
imagine that.
may your rails be high and your cathodes hot...
oh yeah, and your loads resonable.
kg
PMG
Ken Gilbert wrote:
>
> thanks ron, lv, et al. every once in a while i get off my lazy
> duff and actually put something from my head down on the page.
> it's even better when it's somewhat coherent. i hope somebody,
> somewhere gets something out of it. judging by the responses,
> i'd say that happened, which is nice. it's the kind of thing
> that makes me actually want to post more of the good stuff!
> imagine that.
By all means. If it'll help, I'll be overly pesty about something
again, but LV'll have to say I'm full of shit about something first
(that shouldn't be too hard)
Pete
>
> may your rails be high and your cathodes hot...
>
> oh yeah, and your loads resonable.
>
> kg
>
> -----------------------------------------------------------
>
> Got questions? Get answers over the phone at Keen.com.
> Up to 100 minutes free!
> http://www.keen.com
--
JER
from someone's response to it. I also never got the technical post
that many are praising. Sounds like interesting reading. Could
someone re-post it, or E me a copy?
Thanks,
--Jack
>
>
>Ken Gilbert wrote:
>>
>> thanks ron, lv, et al. every once in a while i get off my lazy
>> duff and actually put something from my head down on the page.
>> it's even better when it's somewhat coherent. i hope somebody,
>> somewhere gets something out of it. judging by the responses,
>> i'd say that happened, which is nice. it's the kind of thing
>> that makes me actually want to post more of the good stuff!
>> imagine that.
>>
JER
> Sounds like interesting reading. Could
>someone re-post it, or E me a copy?
>
>Thanks,
>--Jack
>
Someone sent me a copy. Thanks, Jeff.
Nice work Ken.
--Jack
Hans-Juergen Bardenhagen
PMG <av...@mediaone.net> wrote in <3970B6AE...@mediaone.net>:
> I generally say Lord Valve is right about things, but I don't believe
> in the bullshit like the guy who keeps saying "trust in the lord".
> Ok, but nobody shows examples. It's like saying that butter is bad
> for your health, you should eat margarine instead, and then decades
> later, you start hearing that actually, butter is healthier than
> margarine. Well what the f*ck.
Your're right, and I don't understand why this has to be brought
into discussion in such an insulting manner...
> Can anyone come up with an example of running a 4ohm amp with 8ohm
> speakers has caused it to destruct? And can you honestly say there
> are no other factors? And that's one of the things I'm interested in,
> if that amp fell apart from supposedly using too many ohms, what other
> factors were involved. Like I mentioned, I don't see examples.
No, I can't, because I use my Fender Bassman head from 1962 that way
(two 16 ohm Celestion G12 greenbacks wired in parallel) for about 15
years now and it hasn't been damaged yet (volume knob all the way up
to 10, treble and bass down to zero). I should mention that this
Bassman is an export model with a different, but original power
transformer than the US models. The DC voltage in the output stage
of the circuit is around 500+ Volt, by the way.
I even use it the other way round sometimes with an overall load of
2.6 ohm by adding another two 8 ohm G12H Celestions (also wired in
parallel, so this pair makes a 4 ohm load alone). But I'll only do
that if I want to blow the roof of a specific venue... which leads
me to the more interesting part of this discussion: how does it sound?
That "mismatched" load of 8 ohms causes the Bassman to calm down quite
a bit concerning its dynamics and overall output from the speakers.
That's the reason I use it most of the time because not all club owners
like their roof being taken off - and so do my band members, shame
on them... Because what I really like most from my amp is that
unbelievable dynamic translation of what I'm doing on my guitar (a
Tokai Les Paul, by the way), and this can be best heard with a lower
ohm load, meaning either 4 ohms (those two G12H alone) or even with
all four Celestions plugged into it (2.6 ohms). If I should compare
this to the sound of the 8 ohm load, I would describe the latter as
a more compressed, nasal and mid-enhanced tone, something other players
might even prefer instead of my favorite "too loud" sound. Of course
the different types of speakers have their own influence on this, too.
ZZee ya, Hans-Juergen
--
## CrossPoint v3.11 ##
* ZQWKPro v1.2 [unregistered]
Bob
You'd be better off putting some kind of thryristor device designed
for the purpose - a varistor or something, I forget the name but there
are lots of different kinds - even gas discharge tubes.
Dave
impedance from there" thread..."
Sorry, I know I should know about this, but I dont...I'm just a stupid
guitarist...how do I do this? I have a basic analog meter from Radio Shack,
when I tried to measure my cab (I'm not sure i know how to properly measure the
cab or speakers in the first place)...the meter goes from like 0 to 1000 to 10k
ohms or something...not helpful in distinguishing between 4,8,16...would a
digital or other more fancy meter help here? Let me know any helpful hints,
thanks.
Dave
+;-E
Rich Koerner
PMG wrote:
>
> Rich Koerner wrote:
> I think Tiny Tubes provided a link to that page once, it seems to me
> I've seen that before. Prety cool, it melted right through the wall of
> the tube.
Yes, not many have seen something like that.
I also have some EL-34's that a Hiwatt melted also.
> How many of those 400-PS amps actually exist? I never heard of the
> thing until TT started talking about maybe selling one.
I not really sure at this time. There were not in the way of records
keeping around these days. I have some serial numbers of the customers
who had brought them into the shop, and the resent ones that have come
in.
A good customer of mine has started some research on the 400-PS and I'm
working with him to get as much information as possible. I hope to have
a 400-PS Club page in the future with pictures of them with their
owners.
If you all can spread the word about this, give out my URL and e-mail
address, I'm sure it will help putting the missing pieces together.
> Thanks Rich, I saved this to a text file. Ken's was ohms.txt and this
> one is ohms2.txt.
>
> Pete
>
Hey thanks for letting me know that my words are of some value to you.
Help spread the word, and maybe we can put the history of the 400-PS
together.
Bastian
Thanks
Bastian
Robert M. Braught
> Sorry, I know I should know about this, but I dont...I'm just a stupid
> guitarist...how do I do this? I have a basic analog meter from Radio Shack,
> when I tried to measure my cab (I'm not sure i know how to properly measure the
> cab or speakers in the first place)...the meter goes from like 0 to 1000 to 10k
> ohms or something...not helpful in distinguishing between 4,8,16...would a
> digital or other more fancy meter help here? Let me know any helpful hints,
I recommend picking up a cheap digital meter (even one with the
permanently attached leads will do here, approx. $20), assuming you're
not going to be using it very often, and better than 1% accuracy isn't
required either for checking speaker resistances like the thread said.
Be sure to short the leads out before you take your reading and subtract
whatever the 'short' reading is from your speaker test reading. (There
will be *some* resistance in your test leads!)
Hook the leads up 'either way' (polarity is not an issue for speaker DC
resistance). You could use a speaker cable, plugged into the cabinet,
holding the probes *firmly* against the free quarter-inch plug end (tip
and sleeve). This will add the resistance of the speaker cable to your
reading, which can be significant, depending on the cable......(details,
details)
(Do I need to say that the speaker has to be unplugged from the amp for
this to work?)
An analog multimeter, unless it has a very expanded low ohms scale, just
won't let you visually resolve the difference between 4, 8, 16 etc ohms.
(Yes, suitable analog meters do exist, but I thought we were talking
cheap and efficient here.)
An additional noteworthy tidbit is that you'll need to have the speaker
'at rest', meaning don't thump it (mechanically) while you're trying to
take your reading; what happens is that a speaker will generate
electrical energy when the cone moves (including exposure to loud
noise!) that will throw off the reading..........(ain't physics grand?)
Cheers,
Robert
QTS
www.Braught.com
OASYSCO
>impedance from there" thread..."
>
>guitarist...how do I do this? I have a basic analog meter from Radio Shack,
>when I tried to measure my cab (I'm not sure i know how to properly measure
>the
>cab or speakers in the first place)...the meter goes from like 0 to 1000 to
>10k
>ohms or something...not helpful in distinguishing between 4,8,16...would a
>digital or other more fancy meter help here? Let me know any helpful hints,
I assume that you have an analog meter.If so, set the ohms to the 0..1000
setting as you will be measuring a value in that range.
Next, touch the 2 meter leads to each other to determine if you have a bias
that you need to zero out using your thumbwheel - if your unit has one.
To test a speaker, disconnect the leads from the OT to the speaker so you just
have a bare speaker. Connect the pos lead form the meter to the pos terminal of
the speaker; same for the neg side. Yo should get a reading.
To test a cabinet, plug a speaker cable into the cab. On the end not plugged
in, pull/screw back the plug guard to expose the plug and it's pos/neg
connections. Do the same as you did for the speaker.
Greg
andrewunix
:
:A question, When you say:
:"But if you're wondering about how it sounds, and the amp's got good
:trannies
:in it, then mismatch away. Just keep it within ONE TAP please, for
:safety's sake." Ok, "ONE TAP", are you referring to transformer taps
:for speaker ohms? And are they generally 4 ohms apart, and would that
:make running my Bassman at 8 ohms ok? Because, a couple things, 1) yes
No, each tap _doubles_ the impedence of the previous tap.
Most have 4,8,16 taps, and some have 2,4,8 taps.
--
agreenbu @ nyx . net andrew michael greenburg
http://www.nyx.net/~agreenbu/
remove NOSPAM from address to reply.
PMG
Thanks, I was wondering if anyone was going to answer that. "Tap" was a
new term to me, at least applied that way, I thought maybe he was
referring to taps on the xformer, which to me makes sense.
Pete
simply...@my-deja.com
PMG <av...@mediaone.net> wrote:
> Thanks, I was wondering if anyone was going to answer that. "Tap" was
a
> new term to me, at least applied that way, I thought maybe he was
> referring to taps on the xformer, which to me makes sense.
>
> Pete
>
I thought he *was* talking about tranny taps :)
Steve
Sent via Deja.com http://www.deja.com/
Before you buy.
Rich Koerner
Ken Gilbert wrote:
<A much regretted snip>
Keny you just flashed me back to 1965 when I sat in theory class
listening to Mr. "G".
I had the Vertical and Horizontal load line analysis in his class as
part of the study of load line plotting though out his classes.
Damn, he would have been impressed, as well as I am.
I saw LV's comment to you and understand his viewpoint.
Another would be the effects of the back EMF from the collapsing core
field, and the use of clamping diodes.
Your mention of the 470 resistor as a saftey measure I have not seen in
years. Some high end products of years ago had them. But in the
guitar amp game, it would cost too much.
Again Ken, Well Done!!!!
APPLAUSE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Ken Gilbert
the OPT. one tap away represents (in 99% of the trannies out
there) a 1:2 (or 2:1) mismatch from original primary impedance.
~KG~
Ken Gilbert
these nuggets of information:
the first is from stephen connor, a net-bud from across the pond:
>I was obsessed by the tales of destruction when running a
>pentode amp into too high a load impedance, so I had to try it,
>didn't I? The fact of the matter is, I was able to crank a 50
>watt amp wide open into an open circuit and I never got
>anything to arc over or blow up. I can only conclude that:
>
>The plate impedance of pentode tubes (or at least the EL-34s I
>tested) while high compared to the plate load, is still low
>enough to damp kickbacks from the OT somewhat
>
>The NFB helps to reduce the effect by decreasing drive to the
>tubes when the load is removed
>
>However the screens do glow quite prettily and would surely
>melt in a couple of seconds.
>
>Steve C.
the screen's glow goes along with the theoretical prediction of
a great rise in screen current.
RG Keen also pointed out a few things, like the fact that the
unloaded transformer's primary looks like an autoformer, such
that the two voltages on the plate connections are "mirror
images" of one another, symmetric around the B+ voltage of the
center tap. so if the minimum voltage on one side is 50V, and
the B+ is 500, then you can only have a peak of 950V on the
other side.
also the high voltages created by inductive sources are at most
L* dI/dt, or the inductor times the rate of change of the
currrent. this dI/dt is limited by any shunt capacitances in
the windings themselves, which will "soften" the speed at which
the current cuts off. to get a really big voltage peak, you'd
have to have a hard opening of the circuit, like a relay. as he
goes on to say:
>The real danger to an OT is probably a sudden open in a speaker
>line or a sudden open in a tube. That *can* generate a spike
>that punches through insulation.
also, as rich k. sagely pointed out, don't try this kind of
stuff with the really high power amps, like the SVT's or the
400PS's. these amps are running a bit on the edge to begin
with, and you DON'T want to tempt fate.
this has been a very interesting thread.
PMG
Hans-Juergen Bardenhagen wrote:
>
> PMG <av...@mediaone.net> wrote in <3970B6AE...@mediaone.net>:
> > I generally say Lord Valve is right about things, but I don't believe
> > in the bullshit like the guy who keeps saying "trust in the lord".
> > Ok, but nobody shows examples. It's like saying that butter is bad
> > for your health, you should eat margarine instead, and then decades
> > later, you start hearing that actually, butter is healthier than
> > margarine. Well what the f*ck.
>
> Your're right, and I don't understand why this has to be brought
> into discussion in such an insulting manner...
No insult was intended. Word is that LV is not fat, he's just thick
skinned. Or did you think I was trying to insult someone else? At any
rate, I wasn't trying to insult anyone, I was just looking for examples
of an amp that was damaged by running it at 8ohms instead of the 4ohms
it was asking for.
Your example is of an amp that's been used for years the way I wanted to
use my Bassman, and you say there was no damage. Since this thread
started, I've switched to 2-8ohm speakers for 4ohms because I heard so
many bad things about using too many ohms. And I agree, it sounds
better with lower ohms. And yes, it's compressed at 8ohms.
PMG
and provide some links. Unfortunatly I only got 4 files, there's some I
should have gotten but I neglected to, sorry. I should probably dig
them up.
Pete
--
Nnon Amos
1972 - 50 watt - lead - in good condition
sacrifice @ $2,500.00
reply here please
"Rich Koerner" <ri...@timeelect.com> wrote in message
news:39734FF4...@timeelect.com...
Ned Carlson
<guitar...@worldnet.att.net> wrote:
>Thanks everyone. I'm the original poster. Just a little more history...
>the reason I was asking is that I recently finished building a tube amp kit
>(Torres Tiny Tone, 2-12ax7s, 1-6005, 1.5W Amp), and I had the option of
>wiring it up for 4, 8 or 16 ohms. I have a Tone Master 2x12 cab with
>Vintage 30s in it, and that's 16 ohms.
>
>However, it seems like most cabs are 8ohms, so I just wired it up for 8
>ohms. I asked AGA my question cuz I wanted to know if I was damaging my amp
>by hooking it up to the ToneMaster cab.
>
>Looks like the answer is yes.
On a 1.5W amp, it won't hurt much of anything. You've got 1.5W
(probably more like 1W given the mismatch) across 10K ohms,
(5K is what's normally used with 6AQ5, so plugging a
8 ohm output into 16 ohms would be double that) how much
AC voltage is that?
I take it you are either using a very low plate voltage, or it's wired
in triode, a 6AQ5/6005 ought to make about 5W, not 1.5W.
Still, this isn't like a Homer Simpson playing with a nuclear
reactor.
>But I'm still curious about my other question. Okay, suppose you do have an
>amp set up for 16-ohms and you hook up an 8-ohm cab. What kind of
>differences in tone do you get compared to hooking up a 16-ohm cab?
According to you:
>and I had the option of
>>wiring it up for 4, 8 or 16 ohms.
Play it then go back & wire it up for 16 ohms. Where's the problem?
Ned Carlson Triode Electronics "where da tubes are!"
2225 W Roscoe Chicago, IL, 60618 USA
ph 773-871-7459 fax 773-871-7938
12:30 to 8 PM CT, (1830-0200 UTC) 12:30-5 Sat, Closed Wed & Sun
<A HREF="http://www.triodeel.com">http://www.triodeel.com</A>
Tube and Tube Amp info on the net...<A HREF="http://www.triodeel.com/tlinks.htm"> The Big Tube Links Page!</A>
Ned Carlson
<tubegod...@hotmail.com.invalid> wrote:
>So you are saying if my amp is looking for 8ohms and I hook up
>an overall impedence of 4ohms, which is described as being a
>heavier load than 8ohms because the amp has to come up with more
>current,I'd be better off?
Than if you hooked it up to 16 ohms then overdrove it, sure.
You've got this output transformer in there, ya see, and too much
AC voltage can damage it. The output power of a tube does
not have a linear relationship to the *load*, you see, so if you
stick a 16 ohm on the 8 ohm tap of the output transformer,
the AC voltage on the primary is going to go up.
If you don't believe me, measure it for yourself.
In the case of a 1 1/2W amp,given the power & voltage involved
it's very unlikely there would be any problem. Not so on more
high powered stuff.
Hmm, I guess I should call all the
>publishers of electronics refernce materials and give them your
>number...
I got your electronics reference material right here...
"Electronic Guitar Amplifier Handbook, Howard W Sams & Co, Inc"
"Also,they differ in one very important respect; with tube types,
using output transformers, the speaker must NEVER (ed note,
their capitalization) be left off (open) when the amplifier is turned
on" IOW, with too little of a load. People knew this 40 years ago.
Rich Koerner
OK!!!
The 400-PS walked in the door and the smoked socket were not as dramatic
as they can get. These are mild as far as the 4th of July goes.
There is little carbon on the chassis and very minor scorching of the
wires.
So if I get some really DRAMATIC, I'll have them on the page asap.
For now I put the pix on the server for you all to see.
http://www.timeelect.com/test/socket-1.jpg
http://www.timeelect.com/test/socket-2.jpg
http://www.timeelect.com/test/socket-3.jpg
http://www.timeelect.com/test/socket-4.jpg
http://www.timeelect.com/test/socket-5.jpg
http://www.timeelect.com/test/socket-6.jpg
http://www.timeelect.com/test/socket-7.jpg
Now, if anyone wants to disagree with on the fact that any arced socket
should be replaced, they have no experience with RF or Audio Amplifiers
of the magnitude of the 400-PS. Once a carbon path is made, I don't
care how good you clean it up, that spark will find that same place
TWICE!!!!
REPLACE THEM EVERY TIME!!!!
DON'T BE LAZY!!!!!
PMG
Rich Koerner wrote:
>
> OK!!!
>
> The 400-PS walked in the door and the smoked socket were not as dramatic
> as they can get. These are mild as far as the 4th of July goes.
>
> There is little carbon on the chassis and very minor scorching of the
> wires.
>
> So if I get some really DRAMATIC, I'll have them on the page asap.
>
> For now I put the pix on the server for you all to see.
>
> http://www.timeelect.com/test/socket-1.jpg
> http://www.timeelect.com/test/socket-2.jpg
> http://www.timeelect.com/test/socket-3.jpg
> http://www.timeelect.com/test/socket-4.jpg
> http://www.timeelect.com/test/socket-5.jpg
> http://www.timeelect.com/test/socket-6.jpg
> http://www.timeelect.com/test/socket-7.jpg
All the capacitors & resisters around the sockets look kind of toasted.
Do 400-PS always come in looking like that? It gets worse?
Pete
>
> Now, if anyone wants to disagree with on the fact that any arced socket
> should be replaced, they have no experience with RF or Audio Amplifiers
> of the magnitude of the 400-PS. Once a carbon path is made, I don't
> care how good you clean it up, that spark will find that same place
> TWICE!!!!
>
> REPLACE THEM EVERY TIME!!!!
>
> DON'T BE LAZY!!!!!
>
> Regards,
>
> Rich Koerner,
> Time Electronics.
> http://www.timeelect.com
>
> Service * Repair * Modifications * Design Engineering
>
> Live Sound & Studio Production
--
Danny Russell
PMG wrote:
> Your example is of an amp that's been used for years the way I wanted to
> use my Bassman, and you say there was no damage. Since this thread
> started, I've switched to 2-8ohm speakers for 4ohms because I heard so
> many bad things about using too many ohms. And I agree, it sounds
> better with lower ohms. And yes, it's compressed at 8ohms.
Here's my piece. No amount of technical data can prove to any
skeptic that running a higher impedance causes some strange sort of
immediate destruction of all components. The general advice
concerning avoidance of upward mismatches comes from a much more
basic premise, and that is: anybody on this NG that actually repairs
amps daily for a living (tube or SS) will attest to a correllation
between load indifference on the part of the operator, and
electrical breakdown. One person doing an experiment for five
minutes proves nothing. Tens of Thousands of repairs paints a much
stronger picture. If an amp is designed to run within certain
parameters, then deliberately pushing the envelope stresses the
amp. Be aware of the risks. The average failure rate of tube amps
is higher when pushed hard into mismatched loads. But by all means
be my guest and indulge freely, I have plenty of replacement octal
sockets and OT's in stock. -Danny
--
<<<GET BLITZED!!!>>>
http://home.flash.net/~blitz/tunes.html
To get inside my whacky head.
Rich Koerner
PMG wrote:
>
> Rich Koerner wrote:
> >
> > OK!!!
> >
> > The 400-PS walked in the door and the smoked socket were not as dramatic
> > as they can get. These are mild as far as the 4th of July goes.
> >
> > There is little carbon on the chassis and very minor scorching of the
> > wires.
> >
> > So if I get some really DRAMATIC, I'll have them on the page asap.
> >
> > For now I put the pix on the server for you all to see.
> >
> > http://www.timeelect.com/test/socket-1.jpg
> > http://www.timeelect.com/test/socket-2.jpg
> > http://www.timeelect.com/test/socket-3.jpg
> > http://www.timeelect.com/test/socket-4.jpg
> > http://www.timeelect.com/test/socket-5.jpg
> > http://www.timeelect.com/test/socket-6.jpg
> > http://www.timeelect.com/test/socket-7.jpg
>
> All the capacitors & resisters around the sockets look kind of toasted.
> Do 400-PS always come in looking like that?
Most do, Pete.
Mainly because the owners have no clue of the potential that the 400-PS
has.
As with any product you have some do's and don't's. Like most players
out there, the attitude towards such things goes out the window. You
may get away with doing the wrong things on some amps, and on some you
WILL PAY THE PRICE!!!!!!
The 400-PS is one of those amps. If you follow the rules, it's a Great
Amp that is hard on output tubes. This must be kept in mind all the
time with a 400-PS.
User error and/or amp tech error is mostly the cause for the smoked up
sockets.
> It gets worse?
Yes Pete, I have had them in here with a lot more heat damage and carbon
than seen in the pictures I put up on the server. I have had to replace
most of the wiring to all the sockets because of heat damage melting
wires together located more than an inch from where the Flash occurred.
It's a little like the heat given of from an electric arc welder.
You have to remember that the arc remains till the fuse blows. The amp
calls for a 10 amp fuse.
So, just how long is the 400-PS Arc Welder going to keep welding while
trying to blow a 20 amp fuse the owner put in the fuse socket!!!!!!!
Yes, Pete!!!!! They have come in here that way!!!! :(
It's a lot of work and expense because some players and amp techs have a
Know-It-ALL attitude about such things. Then along comes a situation
that escapes them. Rather than hit the books or make an effort at real
thinking, they bad mouth the object of their frustration!!!!!, to
maintain the *illusion* THEY are still on top of their game.
I can't tell you how many times I've heard that tune sung before!!!
Rich Koerner
I had gotten distracted while typing and forgot I had wanted to refer to
one of the pictures in specific.
Look at this picture,..
http://www.timeelect.com/test/socket-2.jpg
At about 11:00 to the tube socket you can see the heat damage done to
the wires running along the socket.
Notice the terminal with the green wire on it is melted. That is pin 7
of the tube socket. Pins 2 & 3 is 2:00 in location with respect to a
clock. Both filament terminals and the plate terminal were involved
here.
The burnt cap had been once connected between the plate and the
kathode. The lead connecting to pin had melted from the kathode pin. I
had moved it out of the way to show the socket damage.
This is really a mild case of damage in this picture.
Simply Steve
damamge what does moderate or major damage look like? I mean it
looks pretty bad to me for mild. What have you seen - big
blackened holes where the sockets used to be?
Steve
Jonathan Krogh
Simply Steve wrote in message
<30cc428c...@usw-ex0103-018.remarq.com>...
>Thanks for the pics, I find them interesting. So if this is mild
>damamge what does moderate or major damage look like? I mean it
>looks pretty bad to me for mild. What have you seen - big
>blackened holes where the sockets used to be?
>
>Steve
>
>
Hahahaha, you just kicked up images of big blackhole voids where the tubes
and/or amp once just stood, or like how the Spinal Tap drummer disappeared
mid-set.
Hans-Juergen Bardenhagen
PMG <av...@mediaone.net> wrote in <39736C9B...@mediaone.net>:
>>> I generally say Lord Valve is right about things, but I don't
>>> believe in the bullshit like the guy who keeps saying "trust in
>>> the lord". Ok, but nobody shows examples. It's like saying that
>>> butter is bad for your health, you should eat margarine instead,
>>> and then decades later, you start hearing that actually, butter is
>>> healthier than margarine. Well what the f*ck.
>> Your're right, and I don't understand why this has to be brought
>> into discussion in such an insulting manner...
> No insult was intended. Word is that LV is not fat, he's just thick
> skinned. Or did you think I was trying to insult someone else? At
No, sorry, you got me wrong, because I didn't clarify what I meant.
I think "Lord Valve" answered in a - let's say - rough way to some
questions in this thread, which I think wasn't necessary. OK, he
knows a lot about amp repairing and he has heard these questions
many times, but that's no reason to put someone else down who
doesn't have his experience. Furthermore there isn't always only
one correct answer to a complex problem. That's why I wrote about
my usage of a 4 ohm amp with different ohm loads.
> any rate, I wasn't trying to insult anyone, I was just looking for
> examples of an amp that was damaged by running it at 8ohms instead of
> the 4ohms it was asking for.
Yes I know, and I don't have those examples, only one where the amp
wasn't damaged for a very long time with heavy usage.
> Your example is of an amp that's been used for years the way I wanted
> to use my Bassman, and you say there was no damage. Since this thread
> started, I've switched to 2-8ohm speakers for 4ohms because I heard so
> many bad things about using too many ohms. And I agree, it sounds
> better with lower ohms. And yes, it's compressed at 8ohms.
I already read about the change you've made, and I'm glad you like
it. But it might happen that you'll get complaints from your band or
someone else about this FAR TOO LOUD SOUND now... ;-)
Do you use two different cabs now? I put those two G12H into my
Marshall 4x12" cabinet, so I have everything I need in a box.
PMG
Hans-Juergen Bardenhagen wrote:
>
> PMG <av...@mediaone.net> wrote in <39736C9B...@mediaone.net>:
[.........]
>
> > any rate, I wasn't trying to insult anyone, I was just looking for
> > examples of an amp that was damaged by running it at 8ohms instead of
> > the 4ohms it was asking for.
>
> Yes I know, and I don't have those examples, only one where the amp
> wasn't damaged for a very long time with heavy usage.
Thankyou.
>
> > Your example is of an amp that's been used for years the way I wanted
> > to use my Bassman, and you say there was no damage. Since this thread
> > started, I've switched to 2-8ohm speakers for 4ohms because I heard so
> > many bad things about using too many ohms. And I agree, it sounds
> > better with lower ohms. And yes, it's compressed at 8ohms.
>
> I already read about the change you've made, and I'm glad you like
> it. But it might happen that you'll get complaints from your band or
> someone else about this FAR TOO LOUD SOUND now... ;-)
The world is very fortunate that I'm not in a band. I have not tried to
be in one for years. I need to run through an Altair Attenuator to keep
the db down.
>
> Do you use two different cabs now? I put those two G12H into my
> Marshall 4x12" cabinet, so I have everything I need in a box.
>
> ZZee ya, Hans-Juergen
What I've got at the moment is an open air cabenet that was built to go
right under a Fender Princeton, that's got an EVM12 in it, and for the
other speaker, I'm using the Fender Princeton that I butchered to hold a
12" speaker years ago, at the moment it's the speaker that I borrowed
from a Champ12. I'm thinking of building a cabinet to hold 2-12"
speakers, and make it about 20"x26" so it would be a good size for the
Bassman to sit on top of, it would be open air.
Pete
--
Next time try shortening it to "BAH" --Dogbert
Rich Koerner
Simply Steve wrote:
>
> Thanks for the pics, I find them interesting. So if this is mild
> damamge what does moderate or major damage look like? I mean it
> looks pretty bad to me for mild. What have you seen - big
> blackened holes where the sockets used to be?
>
> Steve
Well, almost. But, not quite.
When the arc flashes and puts down the carbon path, is now the conductor
that keeps the flash going. It will continue till either the fuse
blows, a wire, or a component supplying the energy to maintain the
carbon arc melts and opens the circuit.
Sometimes, THAT can take a while. Three seconds or more!!!!
I was once working with a friend repairing amps in the early '60s for a
music store. He was working on a Bogen CHB-100 I think. All of a
sudden it started making noise and smoke started coming out of it. My
friend is sitting there watching it smoke, and tells me to look inside
but not directly at it. Sure enough there was a carbon arc sizzling in
the OT at the top edge of the winding.
He said he was just waiting to see how long it would take for the fuse
to blow. Well, it wasn't going to blow. So we had to pull the plug
before the flames started and the owner of the store would have a heart
attack.
Remember, a carbon for even 1 second in a contained chassis can provide
a lot of heat and carbon damage to an amp.
It is not uncommon to see more than one tube socket involved in a
400-PS.
I had one come in the shop that took out four sockets in one shot!!!!!
That was the one I own now. I had cleaned it up before I purchased the
camera I'm using now to that the pictures I have been posting.
Someone asked me what type of camera I was using and now remembered I
hadn't answered that post yet.
I had researched it and came to get the Olympus Camedia Digital Camera
D-360L.
I'm very pleased with it. But, you will go through batteries. If
anyone gets one, get the wall wart and it will cut down the battery
bill!!!!!! :(
Rich Koerner
"Robert M. Braught" wrote:
>
> PMG wrote:
> >
> > Kent Pearson wrote:
> > >
> > > On 15-Jul-2000, PMG <av...@mediaone.net> wrote:
> > >
> > > > And actually, I'd like to hear more about the history of the amps with
> > > > the fried sockets, tubes, capacitors, and xformers. Are we talking
> > > > about amps that were running at 10 for 4 & more hours a day? Are we
> > > > talking about amps that had extreme mismatches in the speaker
> > > > impedance? Are these people who were using 16 or 32 or worse ohm
> > > > speakers in an 4 ohm amp, or are we talking about people who used 8ohms
> > > > into a 4ohm amp?
> > >
> > > Exactly. I've done this many many times over the years with no apparent
> > > problems. Of course, it MUST happen or else we wouldn't be talking about
> > > it. And I certainly wouldn't recommend to anyone. It just that it's never
> > > happened to *me* in all these years. I guess some amps may be more
> > > "durable" (for lack of a better word) than others. Is it possible to fuse
> > > protect against the ill effects described in the quote as being possible
> > > from (accidental) mismatch?
> > >
> > > - KP
> >
> > I generally say Lord Valve is right about things, but I don't believe in
> > the bullshit like the guy who keeps saying "trust in the lord". Ok, but
> > nobody shows examples.
>
> Ok, for example, has anybody had (and confirmed the cause of) the
> Marshall JCM900 (i.e. 2500SL-X) rear panel 'board fry' failure?
> Unfortunately I only end up seeing amps after they're already hurt, and
> when I ask 'how did it happen', I usually only get a nod and a ? stare.
> What I see periodically is one of these where the output transformer
> screen tap connections have arced/shorted at the high/low switch (burnt
> rear panel jacks/switches circuit board); I've always figured this was
> due to mismatch at high volume (I hold Marshall liable for the great job
> of labeling the two position impedance switch: (4)16 or 8 ; I figure a
> user might innocently put a 4 ohm load on the 16 ohm position?)
THERE YOU GO!!!!!!
All because they don't have a three position PC mounting impedance
selector switch.
Talk about a bad engineering design!!!!!
Good thought out engineering takes a back seat to the profit line
again!!!!
And,... That, is my positive statement on this matter!!!!!!