Arcing GZ34???

Post by Jim
I'm kind a bummed because it seems that my Mullard GZ34 in my pre-CBS
Princeton may be bad.
It tests good. It runs just fine in the amp until I push the clean
Princeton (non-reverb) into distortion. At that point, I pop fuses. I
typically use the ground switch hole to install a B+ fuse (when
installing grounded power cord). I popped a 250mA when the fuse was
placed before the filter caps. I do NOT pop a 175mA with it placed at
the OT CT. I popped 1A (standard value) and 1.5A slo-blows at the line.
Substituting in a 5Y3, I don't pop anything. Less headroom with greater
voltage drop.
Substituting a WZ34 Weber Copper Cap, I don't pop anything, and get
plenty of overdrive when pushing with an early DOD 250 circuit or TS808.
The GZ34 is missing the guide pin, and previous knucklehead owner had it
installed wrong, and managed to fry the PT. ...if that can lead to
arcing or other problem.
I'm bummed, because a good Mullard GZ34 is an EXPENSIVE tube.
Are the JJ's reliable at all?

Its possible you have a leaky filter cap section right after the recto
output, or the tube is just not doing its job so well anymore when
asked to deliver current peaks. Could go either way....chicken/egg.
Try a different GZ in the same amp, or try the questionable GZ in
another amp.

If you want to bench the amp and really see what's goin' on, you could
patch in an ammeter with a min/max function before the first filter
and track the current. If the tube arcs and the current is within
tolerable limits, the tube is junk.

Jim

2011-11-25 22:21:54 UTC

Post by boardjunkie1

Its possible you have a leaky filter cap section right after the recto
output,

Been replaced.

or the tube is just not doing its job so well anymore when

Post by boardjunkie1
asked to deliver current peaks. Could go either way....chicken/egg.
Try a different GZ in the same amp, or try the questionable GZ in
another amp.

The Weber SS WZ34 works great.

I'm guessing it is the tube, even though it performs fine until I
purposely overdrive the preamp. A GZ34 should be able to handle
ANYTHING that a Princeton throws at it.

Post by boardjunkie1
If you want to bench the amp and really see what's goin' on, you could
patch in an ammeter with a min/max function before the first filter
and track the current.

I could do that, since I recently upgraded to a Fluke 177.

If the tube arcs and the current is within

Post by boardjunkie1
tolerable limits, the tube is junk.

I could've paid more attention to WHY the PT was fried in the first
place. My goal is to revive, but I'm probably cheating myself out of a
learning opportunity.

All I know is that the guide pin was missing, it was in the wrong
position, and the PT was charred when I got it (bonehead previous owner
had a 7A fuse in it). I replaced all electrolytics and the PT. It only
pops a fuse with the Mullard GZ34, and only when overdriven. I haven't
even looked at the pin-out to figure out the possibilities when
installed wrong (missing guide pin).

I rode it pretty hard the other night with the WZ34. Weber claims it's
a direct replacement for the WZ34, but I didn't recheck B+ or bias. It
sounded nice into the reconed P10Q. The PT didn't heat up, and any
warmth from the OT could've easily been heat from neighboring tubes.

2011-11-26 07:15:10 UTC

Post by Jim
All I know is that the guide pin was missing, it was in the wrong
position, and the PT was charred when

...

Jim, I was going to reply but I'm not sure my previous posts are
getting there. I tried to follow up with you several times about your
Traynor but no response.

Jim

2011-11-27 07:04:11 UTC

Post by Jim
All I know is that the guide pin was missing, it was in the wrong
position, and the PT was charred when

...
Jim, I was going to reply but I'm not sure my previous posts are
getting there. I tried to follow up with you several times about your
Traynor but no response.

Did you post on the Traynor after 11/10? I think that's the last on
that I see. You're saying that your posts are showing? Tell me if I
dropped the ball on a response.

I switched back to working on the Princeton when the old Jensen speaker
was done being reconed. I kind of bounce around a little, whatever I
feel like working on, as spare time allows. The Traynor is actually
sitting on my bench at the moment -- I just haven't started back on it.
I was waiting on a fuse holder (which I now have). I've gotten into
the practice of replacing the pulled ground switches with B+ fuses.

2011-11-27 07:26:28 UTC

Post by Jim
All I know is that the guide pin was missing, it was in the wrong
position, and the PT was charred when

...
Jim, I was going to reply but I'm not sure my previous posts are
getting there. I tried to follow up with you several times about your
Traynor but no response.

Did you post on the Traynor after 11/10? I think that's the last on
that I see. You're saying that your posts are showing? Tell me if I
dropped the ball on a response.

One post from Nov 10 in that thread that mentioned installing a bias
pot, and I asked if you needed help with component values. Also asked
in a thread on ag whether you had seen that post, and what you were
going to do. I figured that it would be good to do while you still had
the Traynor chassis on the bench.

Post by Jim
I switched back to working on the Princeton when the old Jensen speaker
was done being reconed. I kind of bounce around a little, whatever I
feel like working on, as spare time allows. The Traynor is actually
sitting on my bench at the moment -- I just haven't started back on it.
I was waiting on a fuse holder (which I now have). I've gotten into
the practice of replacing the pulled ground switches with B+ fuses.

That's a good idea. Understood about switching projects.

Jim

2011-11-27 20:00:41 UTC

Post by Jim
All I know is that the guide pin was missing, it was in the wrong
position, and the PT was charred when

...
Jim, I was going to reply but I'm not sure my previous posts are
getting there. I tried to follow up with you several times about your
Traynor but no response.

Did you post on the Traynor after 11/10? I think that's the last on
that I see. You're saying that your posts are showing? Tell me if I
dropped the ball on a response.

I must've missed the where you asked whether I saw a particular post.
I've been using the Thunderbird "k" to kill off topic posts, so that
shouldn't happen too much. Otherwise, it's easy to get lost in the
garbage. Believe me, all help is appreciated.

That's a good idea. Understood about switching projects.

2011-11-27 07:55:08 UTC

5AR4's (GZ34's) do that, especially imports. It could be that the
Mullard is just done. There's often a nice fireworks display (inside
the tube). Look for that. Check to make sure that the first cap after
the 5AR4 does not exceed the spec (I don't remember at the moment...40
or 50 uf?... I can check later if you don't have spec sheets). Some
techs have been known to jack up this value, thinking that it will
quiet the supply, but higher values will draw heavier surge currents.
I remember that you know about that, cause you posted calculus
equations for cap charge when The Buffoon didn't know. (Pretty
humorous at the time)

The Mullard 5AR4 is a great tube, probably as durable as any, and it's
favored by audiophiles for its low forward drop. But that's one of the
reasons that I don't use them much in guitar amps; the characteristic
doesn't set them very far from a solid state rectifier voltage-wise
and of course there's little supply sag under load. Not sure if you'd
hear much difference between it and a solid state rectifier. So if you
don't see any merit in higher drop rectifiers for this amp, then
consider staying with the Weber Coppertop.

Post by Jim
Substituting a WZ34 Weber Copper Cap, I don't pop anything, and get
plenty of overdrive when pushing with an early DOD 250 circuit or TS808.
The GZ34 is missing the guide pin, and previous knucklehead owner had it
installed wrong, and managed to fry the PT. ...if that can lead to
arcing or other problem.

That happens a lot.

Post by Jim
I'm bummed, because a good Mullard GZ34 is an EXPENSIVE tube.
Are the JJ's reliable at all?

People like them. I usually use 5U4's or just jump to solid state when
I want more clean headroom.

Jim

2011-11-27 20:30:02 UTC

5AR4's (GZ34's) do that, especially imports. It could be that the
Mullard is just done. There's often a nice fireworks display (inside
the tube). Look for that.

I did, but saw nothing.

However, the existing import 6V6 (Groove Tube Sovtek) was doing it near
the base. Little orange sparkles. Nothing dramatic.

Funny, all the tubes that I end up tossing lately have been Sovtek (they
come in used gear, I don't buy the crap). And a couple of low Chinese
preamp tubes.

Check to make sure that the first cap after

Post by RS
the 5AR4 does not exceed the spec (I don't remember at the moment...40
or 50 uf?...

I installed the "correct" new production multi:
http://www.tubesandmore.com/scripts/foxweb.dll/***@d:/dfs/elevclients/cemirror/ELEVATOR.FXP?item=C-EC20X4-475

Immediate filter is only 20uF.

I can check later if you don't have spec sheets). Some

Post by RS
techs have been known to jack up this value, thinking that it will
quiet the supply, but higher values will draw heavier surge currents.

It's actually quiet at idle. I'm happy with that part.

Post by RS
I remember that you know about that, cause you posted calculus
equations for cap charge when The Buffoon didn't know. (Pretty
humorous at the time)

Ya mean Lord KKK? (The K's refer to the kill thread function in
Thunderbird, but the other meaning is also appropriate.)

Post by RS
The Mullard 5AR4 is a great tube, probably as durable as any, and it's
favored by audiophiles for its low forward drop. But that's one of the
reasons that I don't use them much in guitar amps; the characteristic
doesn't set them very far from a solid state rectifier voltage-wise
and of course there's little supply sag under load.

I was thinking along the same lines. That's why I tried the 5Y3. No
bias pot yet, and I didn't measure quiescent current.

Some guys like the tone from high voltage. Rich Koerner likes to
maximize power and take it from there. He preferred my Super Reverb
with a solid state rectifier. Nothing wrong with that.

My ears tend to prefer lower B+ on amps used for distortion. That's why
I think I like my JMP 2204 compared to JCM 800 (395V on output plates,
compared to around 450+). And with my THD Univalve, I always seem to
gravitate towards the lower B+ settings.

But I'm coming to the conclusion that the Princeton may end up being my
low power clean amp. I might've been happier with a Princeton Reverb,
but this is the project that found me.

Not sure if you'd

Post by RS
hear much difference between it and a solid state rectifier. So if you
don't see any merit in higher drop rectifiers for this amp, then
consider staying with the Weber Coppertop.

I honestly haven't experimented with lower plate voltages in a CLEAN
amp, so I don't know how much of a difference it will make to my ears.

That happens a lot.

So installing the GZ34 with wrong pin orientation CAN fry the PT?

Post by Jim
I'm bummed, because a good Mullard GZ34 is an EXPENSIVE tube.
Are the JJ's reliable at all?

People like them. I usually use 5U4's or just jump to solid state when
I want more clean headroom.

I believe that I also have a couple of spare 5U4.

2011-11-27 22:12:31 UTC

Post by RS
5AR4's (GZ34's) do that, especially imports. It could be that the
Mullard is just done. There's often a nice fireworks display (inside
the tube). Look for that.

I did, but saw nothing.

So the main indicator is the fuse popping. I was wondering if there's
another marginal component, but it's probably just the 5AR4.

Post by Jim
Immediate filter is only 20uF.

You're fine.

Post by RS
I remember that you know about that, cause you posted calculus
equations for cap charge when The Buffoon didn't know. (Pretty
humorous at the time)

Ya mean Lord KKK? (The K's refer to the kill thread function in
Thunderbird, but the other meaning is also appropriate.)

You've actually had much better intuition in several other
electronics- related subjects, including the supposed need for
distilled water to cool dummy load resistors. That was rather humorous
as well.

Post by Jim
Some guys like the tone from high voltage. Rich Koerner likes to
maximize power and take it from there. He preferred my Super Reverb
with a solid state rectifier. Nothing wrong with that.
My ears tend to prefer lower B+ on amps used for distortion. That's why
I think I like my JMP 2204 compared to JCM 800 (395V on output plates,
compared to around 450+). And with my THD Univalve, I always seem to
gravitate towards the lower B+ settings.

I'm with you there, except for when you might want only clean tones
from a given amp. And even then, I'd usually prefer running the B+
lower in order to run bias hotter (keeping dissipation in range).

Post by Jim
But I'm coming to the conclusion that the Princeton may end up being my
low power clean amp. I might've been happier with a Princeton Reverb,
but this is the project that found me.

It's a good amp. Wouldn't necessarily be my own top choice for clean,
but it'll do that at low volume.

Post by Jim
The GZ34 is missing the guide pin, and previous knucklehead owner had it
installed wrong, and managed to fry the PT. ...if that can lead to
arcing or other problem.

That happens a lot.

So installing the GZ34 with wrong pin orientation CAN fry the PT?

I meant that I've seen tubes with broken guide pins plugged back in
with random orientations. Usually there is other damage to the amp,
and it's often due to someone effectively shorting out the fuse.

As for the PT damage, I'd have to check possibilities when the tube is
rotated at random, to see if filaments could bridge B+ or maybe
cathode to filament breakdown. Even without checking, I'd say that's
the likely cause of your PT failure.

Post by Jim
I'm bummed, because a good Mullard GZ34 is an EXPENSIVE tube.
Are the JJ's reliable at all?

People like them. I usually use 5U4's or just jump to solid state when
I want more clean headroom.

I believe that I also have a couple of spare 5U4.

There are other differences between the two tubes, so make sure to
check filament current, etc. Maybe an additional ampere for the 5U4.
If you replaced the PT, then you'll probably have the filament winding
spec on hand.

2011-11-28 10:42:46 UTC

Post by Jim
The GZ34 is missing the guide pin, and previous knucklehead owner had it
installed wrong, and managed to fry the PT. ...if that can lead to
arcing or other problem.

That happens a lot.

So installing the GZ34 with wrong pin orientation CAN fry the PT?

I just took a look at the GZ34 base diagram (hey, I can't remember
everything), and all the active pins are spaced two pins apart. That
means that the two filament pins on the tube would bridge the amp's
filament winding to either side of the B+, or could even short the two
sides of the B+ winding together.

It was Occam's Razor anyway...Very unlikely that the broken base pin
on a tube connected to the power transformer would have occurred
independently of a secondary problem that took out the transformer.

2011-11-27 09:38:53 UTC

Hi Jim,

about the JJ GZ34

My experience with this particular tube was simply dissapointing....

The failure rate some years ago was excessive - 7 out of 10 - although
they were "tested". At first - no problems, but the amps of the
customers came back after a short time. Arcing Rectifiers....

AC30s, Fenders, Sunns....

I really tried to like this tube. Nice and sturdy *looking*; i was
hoping for an alternative to the SINOs....
NOT

I switched to the SOVTEK 5AR4 - with good results.

I don't know whether quality has improved, but the examples a few years
ago where - trash

regards

Jochen

2011-11-27 21:48:35 UTC