replacing tubes
lee
I'm an absolute novice to the Hi Fi world. Recently one of the tubes in the
amp burned out and I need to replace it. The original ones are Svetlana
EL34 and I read that Mullard EL34 is good so I'm thinking about getting one
(or two).
My questions are:
1. Are they compatible, Mullard and Svetlana, cause there are only 7 legs
at the bottom of my Svetlana and I think there are 8 (from pictures) of
Mullard?
2. I often see tubes are sold in pairs, so I guess I need to change them in
pairs. The position of the tubes are, for example, A, B, C, and D. The one
in the D position burned out, so which one (A, B, or C) should I replace in
addition to replacing the one in D position?
3. Should I expect the sound would improve after replacing 2 of the 4 tubes
in my amp?
4. How can I know I'm not getting some remarked or faked NOS as far as
genuinity is concerned?
Please kindly let me have your advice.
Thanks.
Pooh Bear
lee wrote:
> Please kindly let me have your advice.
Get a really good solid state amplifier.
You'll never have to replace any *toobs* ever.
Graham
phatty mo
Yea,just those damn SS bits,that explode to protect the precious fuse(s).
I'm assuming it's a stereo PP amp:
Replace the tubes in pairs- A and B are one channel (left) and C and D
are the other channel (right)
Try to get tubes that are "matched" or measure resonably close.
If the amp has adjustable "fixed" biasing,you'll need to rebias the amp.
Pooh Bear
phatty mo wrote:
> Pooh Bear wrote:
> > lee wrote:
> >
> >>Please kindly let me have your advice.
> >
> >
> > Get a really good solid state amplifier.
> >
> > You'll never have to replace any *toobs* ever.
> >
> > Graham
>
>
> Yea,just those damn SS bits,that explode to protect the precious fuse(s).
A. You're not supposed to connect a short to your amplifier.
B. Few amplifers actually do what you suggest.
C. In the case of a toob amplifier you get the same result by not connecting
the load.
> I'm assuming it's a stereo PP amp:
> Replace the tubes in pairs- A and B are one channel (left) and C and D
> are the other channel (right)
>
> Try to get tubes that are "matched" or measure resonably close.
> If the amp has adjustable "fixed" biasing,you'll need to rebias the amp.
Ahhhh... the 'joys' of having to play technician to get decent results !
Do you like playing steam loco driver too ?
Graham
pf...@aol.com
A couple of things to keep in mind:
Tubes wear out, they seldom "burn out" at least in the sense of an
electric lightbulp where the filament goes 'phtttt'. So, if your
tube(s) did actually burn out in that sense, it is quite likely that
something else is going on to be checked before you simply replace the
tubes.
You have not told us anything about your amp, age, type, maker,
maintenace nor any of the other information that would be helpful to us
to help you out. Nor even if it is stereo, mono, or guitar... although
the latter is unlikely if you use the term Hi Fi.
However, and in a vacuum: Modern "Mullard" tubes are no better nor
worse then Svetlana tubes, they are more-or-less the same tubes, but
with the old name on the new box. In general, the only advice I give to
people purchasing recent-manufacture tubes is "stay out of China".
Otherwise, the differences are mininal. They are mutually compatible,
yes.
As to replacing tubes, clearly you do not have a tube tester capable of
even basic matching, or it is unlikely you would be asking questions
here. So, replace output tubes in any given channel as matched pairs...
but make sure that what you get is actually 'matched', and not merely
from the same lot and batch as is typical from some sellers. Matching
in the proper sense is a series of several electrical parameters and
operating conditions, including but not limited to: Plate current,
Gmhos at a specific bias, and filament current at a fixed voltage, both
within 5% of each other, and within the tube specifications, and
hopefully after some period of 'burn in'. DON'T replace *just one* tube
unless you have the ability to determine that the other(s) are good and
at least reasonably close to the replacement. Most amps will tolerate
mismatching to a considerable degree, but it is not a good idea in
general.
You have no assurance of a truly original tube other than the
reputation of the seller and if you have some expertise in what they
should look like.
You should most definitely expect an improvement in sound.... IF....
tubes are your only issue. But... Make sure, again, that is the only
issue.
Yes, as others have mentioned, do pay attention to the bias. On most
HiFi amps, it is adjustable, some make it obvious, some do not.
Ignore Graham. What he may have to write is 'true', but not 'relevant'.
Peter Wieck
Wyncote, PA
pf...@aol.com
1. Define "really good".
2. Describe what happens to your speakers when the amplifier as
described above is driven to clipping.
3. Describe what happens to the amplifier as described above if it is
run with input, but without a load.
It is a matter of 'pick your poison'. Each system has its advantages,
each system has its risks. When a solid-state amplifier goes into
melt-down for whatever reasons, it has the capacity to fry your
speakers as well as itself and in short order. Tube amps seldom fry
speakers as they cannot send straight DC through the output
transformers (to, but not through), they usually just destroy
themselves.
When a tube amp 'dies', there are remarkably few components to
consider. No chips involved, 7 - 10 tubes, and three transformers, a
dozen caps, two dozen resistors, about it. Maybe a SS diode, maybe a
choke or two. When an equivalent SS amp 'dies', it gets a lot more
complicated as the cascade effect can go all the way back to the
power-supply, and we haven't even mentioned chips. Proper fusing will
protect the transformers on Tube amps, no amount of fusing in a SS amp
will protect the circuitry as the nature of the beast simply does not
allow that and proper function. One's speakers ---perhaps--- But if the
amp chooses to crap out and send DC to the speakers, that fuse won't
help.
And, anyway, if you are so "anti" tube, why are you here other than to
be a PITA?
Peter Wieck
Wyncote, PA
Patrick Turner
Pooh Bear wrote:
So how come I get so so many solid state amps that need a $120 fix to
replace blown
output transistors?
I have so many of these critters they weigh down my shed sometimes....
They kids turn up the volume at the end of school year party, wow, dad's
old
amp sure CAN go loud, cool eh.
Shit, what's that smoke coming out of the old AR9's?
Gee, how come its distorted? Hey, who turned off the amp?
Yeah, SS amps suck alright, they blow a speaker, so a speaker fights
back with a
jammed voice coil, the fuses in the amp ask the transistors to die
first, which they do,
and finally the rectifier blows and the fuses......
I had a couple of whole systems to fix last year, those parties were
very expensive, new speaker drivers,
re-doing the crossovers that were fried, repaired amps, lots of fried
bits.
Does anyone really like direct coupling?
Of course when a tube does bow out, one should ALWAYS find out why
before
just plugging another one in, because there may well be some reason
WHY that tube died, such as a loose grid pin gripper in a tube socket,
faulty cap etc.
45 year old tube amps often have a multitude of accumulated faults which
should all be fixed.
But when that's done its amazing how well they last using modern caps
and resistors.
45 year old solid state amps should be chucked into the dumper bin.
Patrick Turner.
a
Patrick Turner
Pooh Bear wrote:
> phatty mo wrote:
>
> > Pooh Bear wrote:
> > > lee wrote:
> > >
> > >>Please kindly let me have your advice.
> > >
> > >
> > > Get a really good solid state amplifier.
> > >
> > > You'll never have to replace any *toobs* ever.
> > >
> > > Graham
> >
> >
> > Yea,just those damn SS bits,that explode to protect the precious fuse(s).
>
> A. You're not supposed to connect a short to your amplifier.
Some people just can't help it.
The frayed speaker wires at the rear of most amps cause many failures.
People turn on the system, not loud, don't realise there is a short, and
a silent/distorty channel, so after 10 seconds, one SS channel just dies, no
warning.
A tube amp gets all hot and bothered, tubes go all red, and that looks bad,
so chances are an owner turns it off, and asks himself what is wrong.
He gets more than 10 seconds before it is too late....
>
> B. Few amplifers actually do what you suggest.
Oh yes they do.....
>
> C. In the case of a toob amplifier you get the same result by not connecting
> the load.
Nope, not if the tube amp is well made.
Well made tube amps are unconditionally stable and will not blow up
if left turned on without a load; its a silly myth.
Some old and poorly designed amps would oscillate without a load,
but not all the well made ones.
>
>
> > I'm assuming it's a stereo PP amp:
> > Replace the tubes in pairs- A and B are one channel (left) and C and D
> > are the other channel (right)
> >
> > Try to get tubes that are "matched" or measure resonably close.
> > If the amp has adjustable "fixed" biasing,you'll need to rebias the amp.
>
> Ahhhh... the 'joys' of having to play technician to get decent results !
Well, its better than acting as a solid state undertaker when you realise its
better to junk
the SS amp rather than fix it.
>
>
> Do you like playing steam loco driver too ?
Not while he's out sailing round the bay in his yacht....
Patrick Turner.
>
>
> Graham
Patrick Turner
"pf...@aol.com" wrote:
> Lee:
>
> A couple of things to keep in mind:
>
> Tubes wear out, they seldom "burn out" at least in the sense of an
> electric lightbulp where the filament goes 'phtttt'. So, if your
> tube(s) did actually burn out in that sense, it is quite likely that
> something else is going on to be checked before you simply replace the
> tubes.
Correct, but some tubes do "burn out", if the grid pin becomes
disconnected,
or bias failure occurs.
Our hi-fi beginner friend will soon get used to looking after his gear if
he cares for it,
and desires it to last; perhaps he will talk to the sensible types amoung
us, and
notice that we care about all the things we have, and never take anything
for granted....
>
>
> You have not told us anything about your amp, age, type, maker,
> maintenace nor any of the other information that would be helpful to us
> to help you out. Nor even if it is stereo, mono, or guitar... although
> the latter is unlikely if you use the term Hi Fi.
With luck he will ignore Graham, and WILL NOT get a solid state amp,
and he will tell us more...
>
>
> However, and in a vacuum: Modern "Mullard" tubes are no better nor
> worse then Svetlana tubes, they are more-or-less the same tubes, but
> with the old name on the new box. In general, the only advice I give to
> people purchasing recent-manufacture tubes is "stay out of China".
> Otherwise, the differences are mininal. They are mutually compatible,
> yes.
The genuine Svetlana "winged C" are what he could use to retube, and he
should have few regrets.
>
>
> As to replacing tubes, clearly you do not have a tube tester capable of
> even basic matching, or it is unlikely you would be asking questions
> here.
If the set of tues he has is old, replacing all with a matched quad isn't a
bad idea.
He will have 3 spares.....
Since an EL34 is only the same price as cheap restaurant meal, the
tubeophile should not complain
about the cost, which is real terms is cheaper than ever before compared to
north american average weekly earnings.
The tubophile will be passionate about having things right, and checking
things out,
and know someone who really is a good tech who won't rip him off,
so that when replacing output tubes, the tech will search around for any
causative problem.
Preventative maintenance should be done.
> So, replace output tubes in any given channel as matched pairs...
> but make sure that what you get is actually 'matched', and not merely
> from the same lot and batch as is typical from some sellers. Matching
> in the proper sense is a series of several electrical parameters and
> operating conditions, including but not limited to: Plate current,
> Gmhos at a specific bias, and filament current at a fixed voltage, both
> within 5% of each other, and within the tube specifications, and
> hopefully after some period of 'burn in'. DON'T replace *just one* tube
> unless you have the ability to determine that the other(s) are good and
> at least reasonably close to the replacement. Most amps will tolerate
> mismatching to a considerable degree, but it is not a good idea in
> general.
Some amps do not need matched tubes, and all that use individual auto or
cathode bias don't.
It's better that pair of tubes in output stages are bought as matched pairs
though.
The closer the match, the lower the 2H distortion. But in many amps the
results of
using mismatched tubes is not a problem since the distortion at normal
listening levels is low anyway.
Amps with just one bias voltage applied to all the grids DO NEED matched
tubes.
The trouble is that after a few years the tubes become unmatched.
Tubes that were un matched to begin with might drift further apart, or
drift
towards each other in characteristics; Amps used every day should be
serviced each year.
>
>
> You have no assurance of a truly original tube other than the
> reputation of the seller and if you have some expertise in what they
> should look like.
>
> You should most definitely expect an improvement in sound.... IF....
> tubes are your only issue. But... Make sure, again, that is the only
> issue.
If the output tubes are tired, maybe the driver tubes are also tired....
>
>
> Yes, as others have mentioned, do pay attention to the bias. On most
> HiFi amps, it is adjustable, some make it obvious, some do not.
There are many amps where there is no indication that the bias condition is
faulty,
or poorly adjusted.
>
>
> Ignore Graham. What he may have to write is 'true', but not 'relevant'.
Graham is a stirrer, and someone should give him a wooden spoon
and a bucket of mud, and leave him to it up the back yard........
Patrick Turner.
>
>
> Peter Wieck
> Wyncote, PA
Lee
You see, I know nothing about electricity, magnetism or anything like that.
I probably used the wrong word when I said burnt out. To be specific, I
first noticed some hissing sound on the left side, so I checked the cables
and they were OK and then I saw one of the tube didn't "glow" inside my amp,
that's what happened. So I thought it burned out in the sense of an
electric lightbulb goes out. Please forgive my stupidity.
My amp is a Copland 401 bought approx 8-9 years ago and I use it every now
and then. In all these years, I never did anything to it except turn it on
and play my music. I usually leave the power on (for months) to keep it
'warm'. That's what my friends told me.
I never thought about something wrong in the amp that caused the tube to
"die". I thought it just aged enough to "die". Do you suggest I should
check anything else?
Somebody in the shops I visited today also mentioned that I need to re-bias
my amp. I notice there are 2 dial labelled "Left/Right Bias Balance" on the
mainboard, should I simply turn those dial until both sides sound balanced
by using my ears or I need some tools/devices to rebias the amp? Is that
something I can do at home by myself?
Again, please excuse me for being a total idiot and asking questions that
might sound stupid to you.
Thank you very much.
<pf...@aol.com> wrote in message
news:1139231006.7...@z14g2000cwz.googlegroups.com...
pf...@aol.com
Funny thing about that.
I keep a little live-steam yacht, about one meter long, two-cylinder,
lever reversible engine & butane-fired boiler. Sounds like a sewing
machine in heat when it runs.
Clever, these German toymakers.
Peter Wieck
Wyncote, PA
pf...@aol.com
You see, I know nothing about electricity, magnetism or anything like
that.
I probably used the wrong word when I said burnt out. To be specific,
I
first noticed some hissing sound on the left side, so I checked the
cables
and they were OK and then I saw one of the tube didn't "glow" inside my
amp,
that's what happened. So I thought it burned out in the sense of an
electric lightbulb goes out. Please forgive my stupidity.
_____________________________________
Didn't you know? Electricity is magic.
That said, nothing you wrote was stupid. What I am looking for are
indicators as to what is going on so that the advice given is apt. So,
one tube is dark.
My amp is a Copland 401 bought approx 8-9 years ago and I use it every
now
and then. In all these years, I never did anything to it except turn
it on
and play my music. I usually leave the power on (for months) to keep
it
'warm'. That's what my friends told me.
____________________________________________
These are Friends? Unless one is listening actively the system should
be shut off. Those few systems that need quiescent supplies usually
have them built in. Those that don't, don't.
I never thought about something wrong in the amp that caused the tube
to
"die". I thought it just aged enough to "die". Do you suggest I
should
check anything else?
____________________________________________
If these tubes were running 24/7 for months at a time, it is possible
that they (it) died from age. All other things being equal, that is. I
know of several EL-34-based amps that run in that mode, which have not
died.... yet. More on this later.
Somebody in the shops I visited today also mentioned that I need to
re-bias
my amp. I notice there are 2 dial labelled "Left/Right Bias Balance"
on the
mainboard, should I simply turn those dial until both sides sound
balanced
by using my ears or I need some tools/devices to rebias the amp? Is
that
something I can do at home by myself?
______________________________________________
Yes, you can do this at home by yourself. You need to have the proper
instructions from the maker and the test-points where you measure the
voltage. This is not a 'by-ear' adjustment in most case (it is, in
some), but something that should be done with a fair amount of care,
and with an accurate meter. I am sure someone here familiar with that
amp (I am not) could give you the procedure, chapter and verse. The
only tool you need is a VOM.
Again, please excuse me for being a total idiot and asking questions
that
might sound stupid to you
_______________________________________________
The only stupid question is the one you don't ask. All the rest are
valid.
So, on tube replacement. As Patrick suggests, and as your
method-of-operation suggests, all the tubes in your amp are likely
worn. If you can afford it, replace them all from end-to-end. As
Patrick suggests, the worst that can happen is that you have spares.
The output tubes should be matched. A matched Quad will not set you
back any-much-more than two matched pairs, so you may as well indulge.
The driver tubes don't matter as to matching. Svetlana tubes are fine
from end-to-end, spend money on the tube, not the box it came in.
Get the operating instructions for that amp, and get the bias procedure
down. Do it about every 5 hours of use for the first 30 hours or so, to
allow for burn-in and normal drift.
For the first 5 hours of operation, watch the amp like a hawk for any
signs of trouble. Since I really don't know how old it is, if it is
well-and-truly 40+ years old, I would do all the small-value caps
(non-electrolytics) anyway. This, too, you can do at home with a
soldering iron and the Mouser 800-number to order parts. NOTE: Voltages
in a tube amplifier can be lethal. NOTE: Tubes get very hot. Use
precautions, and don't work with an amp that is plugged in unless you
have the proper equipment and take the proper precautions. Did I
mention: Be careful.
But, if this is a fairly-recent vintage amp, likely the tubes are all
that is necessary. Run it when you need it (allow perhaps-10-minutes
after each turn-on for it to sound best), and the tubes should last you
many years. Tubes are like light-bulbs inasmuch as the turn-on shock is
the single most direct cause of filament failure over time. But also,
and exactly like light-bulbs, when running, they don't like physical
shock. So, if the amp was inadvertently bumped at some time when it was
just sitting there 'on', that could have done it. But
all-things-being-equal, the filaments in these beasts is the last thing
that fails, excepting abuse. So, save your power unless you need the
tubes to heat the room. As a complete aside, there are certain tubes
that if run without a 'load', will deteriorate in function to the point
of becoming useless. Mostly these are not power-output tubes but
small-signal and RF tubes, however the principles remain the same. The
6AQ8 used in many FM front-ends is notorious for this behavior.
As Patrick also suggests, about every 200 hours of actual use, check
the bias anyway. Or once a year, again anyway. There is no need to
willy-nilly replace tubes on a scheduled basis as you are likely
neither a hospital nor a broadcast facility where lives or income
depend on optimum performance. Replace them when the bias starts to
drift badly and cannot be stabilized, where it cannot be adjusted to
the necessary limits or from other signs of wear. This is no more than
what one would do with any amp, clean the controls (if any), and
generally check for signs of problems.
Let us know if you have any other symptoms... and, if by any chance,
any of the tubes starts to glow cherry-red at the plate(s), shut it
down FAST.
Good luck with it. It isn't rocket science, so don't get too worried
about it.
Peter Wieck
Wyncote, PA
lee
Your advices were very helpful.
Would anyone suggest where I could find the re-bias procedures and related
information? I tried to search the Internet but there are not much about
Copland 401; probably it was too old and was not popular, or I just didn't
know where to search.
Best regards.
<pf...@aol.com> wrote in message
news:1139249794.6...@g43g2000cwa.googlegroups.com...
bart
> Thank you again.
>
> Your advices were very helpful.
>
> Would anyone suggest where I could find the re-bias procedures and related
> information? I tried to search the Internet but there are not much about
> Copland 401; probably it was too old and was not popular, or I just didn't
> know where to search.
>
Exercise caution around tube amps.
The article describes a 402. Compare and see how similar it is to your
401.
Web site:
Contact one of the distributers for assistance...
pf...@aol.com
Go with Bart's advice on this one. The 402 looks close to your amp and
uses the same output tubes. Start there until you get the *exact*
procedure for you 401. But it really looks like it will be nearly/just
the same.
Peter Wieck
Wyncote, PA
p.s.: setting bias by measuring in millivolts is one of the best uses
of good-quality analog meter as the needle will not jump all over the
way digits do. My Fluke digital meter does have a smoothing function
for that as well as an 'analog' bar graph, but I do miss my old Simpson
at times.
lee
I looked at the main board and couldn't find things as mentioned in the
article. However, I was able to find the schematic of 401 at
www.drtube.com/schematics/ copland/cta401.gif. I also found a guy who run
into same problem as me, but that was 6 years ago and there wasn't a
solution in the thread.
http://groups.google.com/group/hk.rec.audio-visual/browse_frm/thread/c5abb9b45aadcfba/1c285b68edd68b88?lnk=st&q=copland+401&rnum=2&hl=en#1c285b68edd68b88
I also tried to contact the guys in that conversation, but no reply, I guess
the email addresses are not valid anymore.
To put myself on the safe side, what would happen if I rebias the amp
incorrectly or not rebias at all?
Thanks a lot.
<pf...@aol.com> wrote in message
news:1139340391.6...@g14g2000cwa.googlegroups.com...
pf...@aol.com
>my amp. I notice there are 2 dial labelled "Left/Right Bias Balance" on the
>mainboard, should I simply turn those dial until both sides sound balanced
>by using my ears or I need some tools/devices to rebias the amp? Is that
>something I can do at home by myself?
Looking at the schematic, I would speculate that P1 & P101 (Left &
Right Bias Balance) are the bias pots, and per the schemactic you want
480mv (0.48VDC) at Pin 8 of the tube. It looks like there is one bias
pot per channel, and you measure at both tubes in each channel at Pin
8. But also note that by adding bias to one tube, you take it from
another, so you _DO_ have to measure both tubes at Pin 8 to make sure
that you get the split at exactly the correct voltage, don't just go
with one. If the voltage is too high (more than 0.96VDC (960mv) in
total, you will have to adjust P3 at the power-supply as that controls
the overall voltage available. I do not know if there is a P103 (which
would assume two separate power-transformers) but if so, then there are
two pots (one bias, one voltage) per channel. Otherwise, only one
voltage pot to serve both channels and one bias pot per pair of EL34s.
It is not very likely that you will have to adjust P3, but obviously it
is there for a reason.
As you finish with one channel, check the other, back and forth several
times until both read identically and steady.
You do know two things: First, that the bias is adjustable. Second that
it served you for a number of years with the bias as you found it. So,
you have at least a fighting chance that what is already set is
reasonably OK.
What _can_ happen if the bias is wildly off is that you can either
destroy the new tubes pretty fast or the amp can go into runaway...
both are extremely unlikely. But the overall service life of the tubes
is greatly affected by bias, and therefore it should be done especially
with new tubes during the burn-in process.
You have two active choices at this point: Wait until you get the
precise procedure from Copland, or follow the schematic to get the
voltages shown. If you are not in a hurry, I would wait. That would
mean _not_ using the amp with the new tubes until you get that
information. Of course, you could always assume that the bias-in-place
is reasonably good (the passive choice) and go with that. But if you
take this choice, you should STILL search for the proper procedure and
do it as soon as you get it. The crude analogy is like purchasing a
used car from a private party and assuming that it had a recent oil
change and tune-up.
Peter Wieck
Wyncote, PA
lee
who showed the other side of the story :)
Unfortunately, the official Copland web site doesn't even have their contact
information. So I need to go to the local distributor to see if they are
willing to help. Hope they won't just try to sell me a new amp. If I'm
lucky, hope I could get the official rebias procedure from Copland before I
could go any further.
Definitely will post here again when I got any new questions.
Thank you again everyone!!!
<pf...@aol.com> wrote in message
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