Bad Sozo caps???

[dehughes]

Several months back I purchased a set of Sozo Vintage Mustard capacitors for my Germino Classic 45 (JTM-45 clone). They sound GREAT.

However, I noticed that ever since they were installed, the amp periodically thins way out....major loss of low end and some overall volume....and this is only remedied by turning the amp to standby and then back on again. I have tried the following: different channels on the amp, different eq and volume settings, installed known good tubes, tried different guitars, different cables, different electric outlets, and even a different building entirely. Nothing has eliminated the problem. Granted, it is relatively infrequent (maybe happens once every few times I play the amp), but it never happened before the caps were installed. I sent the whole amplifier into Greg Germino and he tested the caps and went through the entire amp, and found nothing amiss. The caps tested out fine and the whole amp was gone over, and he play-tested the amp extensively with no issue. He said he'd experienced such a thing before when he first started using Sozo caps, and found that when he installed the supposedly problematic caps in another amp, it ran fine with no issues...and he was baffled as to what the cause might have been.

Is this part of the natural break-in of these type of handmade caps? I've used the standard Sozo caps and never experienced any problems, so I'm unsure. As well, the caps are the only constant in this equation, so I'm fairly certain the issue lies with them. Before I go order new caps and begin a lengthy process of elimination, I was wondering if you all had any ideas as to what the problem might be?

[soundmasterg]

I've never heard of anything like that being caused by bad coupling caps that wouldn't show up when testing caps. I've used Sozo caps myself and never had any problems of that nature, though I've only used the standard Sozos myself. I would suspect it is something else causing it...an oscillation or something of that sort. If you still think it is the caps, then what you can do is try to play the amp outside of it's box so you can access the circuitry easily. Measure everything in the circuit around those caps....especially the DC voltage at various points in the circuit, even grids where there should be nothing. Then when the problem occurs, don't put the amp into standby...measure the DC voltages again and see if anything has changed. If a cap was bad, it would be leaking DC to a stage following it. If you had a signal generator, you would also put a steady 1KHz signal in and measure the AC voltage and compare too. If you had a scope, you could try to find the problem on a scope as you stick a signal in. It could be something as simple as a socket that needs to be retensioned too...or a bad volume pot. Another possibility is a bad solder joint or an intermittant ground connection somewhere. You and I are local to each other so feel free to PM me and you could come by and have me take a look if you want. I do start back up with school next week however, so I will get busy quickly.

Greg

[dehughes]

Killer. Thanks Greg! I'll definitely welcome your advice and help....and if I do end up coming out there at some point I'll be happy to buy beer or some other offering for your troubles. I'm without an oscilloscope, but I do have a decent DMM and a bit of OCD to go along with. Hopefully I can find a fix that is evident and simple.

I too thought about other things like solder joints, etc...and I was hoping to not have to do extensive testing on it, but I may have to if it's going to be problematic. What's more, nothing was tinkered with outside of the cap swap, at least, when I did it. When the amp went in to Greg he replaced a bunch of resistors and tested it all out. The amp was mostly trouble free once it came back, and it wasn't until recently that it's started to crop up again (maybe 3 times in the past 3 months).

One thing that you mentioned....Oscillation. Elaborate on that, please, for this comes to mind:

Let's say this "issue" has manifested itself 10 times. Out of those 10 times, about 5 of them found me playing with a delay pedal and various other effects and generating strong, low-end pulses. I noticed that once when I was doing this same thing with my Princeton (6G2), I worked the front end pretty hard and the amp seemed to "fade" a bit...not as drastic as the Germino, but it definitely "felt" like it took a hit and then needed a few seconds to "stabilize". The Princeton has never done anything like that before, and never since.

What's more, I know that the JTM-45 is an inherently BASS HEAVY amp (it's basically a Bassman circuit, anyway), so this all has me wondering if there might be some sort of broadening of frequency input to the (power?) tubes that comes with the Sozos, and any excessive low frequency information might be causing "things" to get out of whack in one or more stages....kinda like getting the wind knocked out of you. I'd really head that direction for a concrete explanation of the problem, save for the 4 or 5 times out of 10 where I was simply playing my guitar sans effects and the "issue" manifested itself.

[Jazz P Bass]

You should check the grid side voltage after the caps that you installed.
My bet is that they are leaking.
Exactly where in the amp circuit are these caps located.
That information may help in identifying the true nature of the problem.

[dehughes]

All .022 and .1uf caps are the Sozo Vintage Mustards.

Greg Germino himself tested them and said they're good, so is it possible they'd test out fine but still leak in such a way to cause what I'm experiencing?

[Jazz P Bass]

What circuit are they in?
I do not know how they where tested.
In the amp the cap may have 300Vdc on it.
You need to troubleshoot the amp.
Period.

[dehughes]

I summed things up pretty well in the first post. I'm not sure what Greg used to test it, but I figure the guy builds these things for a living so I wager he did a good job of testing it.

Now, if I understand cap testers, they don't put 300+ volts on the cap to test it, so it is possible that under full power they are getting squirrely. I'll take the amp out of the cabinet sometime next week and see if I can get it to be funky while the chassis is exposed, and then test the caps for DC leakage.

[Chuck H]

Is it possible to induce the problem or is it random? That is, does it only happen when the amp is cranked, has a certain pedal in front, certain guitar, on a particular channel, etc.?.

[dehughes]

Is it possible to induce the problem or is it random? That is, does it only happen when the amp is cranked, has a certain pedal in front, certain guitar, on a particular channel, etc.?.

I've tried to induce the issue, but I've yet to find a specific permutation that brings it about. Tried cranking, tried hitting it with lotsa crazy effects, tried different guitars, tried different EQ settings....all to no avail.

[HTH]

if its a JTM45 clone, there ain't that many caps in the amp - it would be worth subbing in some other caps just to be sure, then at least you know. its a PTP amp so replacing the caps ain't no biggie.