Problem with my g*itar tube amp?

__HM__ · #1 08-25-2010, 07:11 PM

I have a Traynor 2x12 80w combo all tube amp. 3 pre tubes, 4 power. A while ago, it started squealing, which Im led to believe by google is a preamp tube issue, and that one of my pre tubes had gone "microphonic." This problem had been happening off and on for weeks.

So I finally replaced all 3 of my preamp tubes with GrooveTube golds, fearing it would squeal in the middle of a show I had to play, and the problem stayed at bay for 3 days. Now, it's happening again. Is it possible that its a power tube problem? I highly doubt one of those pre tubes died after only 3 days. the power tubes came in the amp, and it is a 2008. So It's very possible that one or more of them is bad. But I didn't think power tubes squealed like failing pre tubes do?

Advice? Any feedback is appreciated! Thanks!

Tusec · #2 08-25-2010, 08:01 PM

You're right that output tubes don't squeal. And apparently it wasn't a preamp tube since you replaced them and it's still there.

Does it squeal randomly or is related to something else -- like can you make it squeal by ramping up the volume? A microphonic preamp tube will usually only go into squealing feedback when the volume or gain is set high.

I wonder if an intermittent bad filter cap could let the preamp signal ride around the supply rail into places it shouldn't go and cause positive feedback = squeal.

I once had an amp that would have crazy blasts of random very loud squealing that turned out to be an input jack that wasn't achieving a solid ground when nothing was plugged into it.

KramerBassFan · #3 08-25-2010, 08:03 PM

Have you tried it with different cords and cables?

Its possible you have microphonic pickups.

__HM__ · #4 08-25-2010, 08:15 PM

the louder the volume or gain, the louder the squeal. It becomes significantly more noticible when the lead/gain channel is switched on.

Edit: Its definitely not a cord, as it happens randomly, in the middle of playing. The problem persists with all 3 of my guitars.

Tusec · #5 08-25-2010, 08:23 PM

Can you make it happen with nothing plugged in?

Does it do it when you're plugged in but not playing? Can you make it quit if you turn the guitar volume down?

__HM__ · #6 08-25-2010, 08:25 PM

with nothing but power going to the amp, it's perfectly audible.

Tusec · #7 08-25-2010, 08:29 PM

Quote:

Originally Posted by __HM__

the louder the volume or gain, the louder the squeal.

If it's affected by the gain knob then it's early in the preamp, probably in the first gain stage. Or it's prior to the preamp -- in the jacks, cord, or guitar.

Are you using any pedals?

Tusec · #8 08-25-2010, 08:32 PM

Quote:

Originally Posted by __HM__

with nothing but power going to the amp, it's perfectly audible.

Okay, so it will sit there and squeal with nothing plugged in, and the gain control makes it louder or quieter.

What happens if you bang on it with your fist?

What happens if you plug something into the second jack that you never use?

__HM__ · #9 08-25-2010, 08:34 PM

Well, the problem is off and on, and it just fixed itself. it seems to only act up when it's at its hottest. But really the problem's pretty random. Since the problem isnt occurring right now, I can't test banging on it. and as for a 2nd jack, there isnt one. Not for input, at least.

Tusec · #10 08-25-2010, 08:41 PM

Can you make it *start* squealing by banging on it? If you can then it's something mechanical like an iffy solder joint or cracked trace on a board or something. You might also try wiggling the first preamp tube (the one farthest from the power tubes) while the amp is on to see what that does (If you just touch the tip of it it won't burn your finger).

__HM__ · #11 08-25-2010, 08:47 PM

neither of those tips did anything :/

Tusec · #12 08-25-2010, 08:56 PM

Hmm, well, I'm out of bullets. Intermittent problems are the trickiest to troubleshoot. Maybe someone else will have a good idea but I think it's likely you'll need to take it to a tech so he can poke around in there and try to flush the problem out.

__HM__ · #13 08-25-2010, 09:29 PM

Any idea where I could take it? Im near cincinnati... I wouldnt know where to start.. lol.

BassmanPaul · #14 08-26-2010, 10:33 AM

It would be helpful if you told us what amp it is.

Squeals and other noise can have many roots. It's likely you have a bad decoupling cap in the amp somewhere. These prevent AC signals from getting into other stages via the power supply. If one is faulty you can have noises from low frequency chug chugs (motorboating) to high pitched screams. A microphonic tube is easily detected by tapping on the glass envelope with a pencil. You will hear the clunks through the speakers. These cause trouble by feeding back like a microphone to the speakers. Even a brand new tube can be microphonic.

Paul

chicago_mike · #15 08-26-2010, 10:49 AM

Pull the preamp tubes. Leave the power and the phase inverter tube in the amp. Power on. Hows the noise? How's the squealing?

Put the 1st channel preamp tube in...check noise and squealing..tap on tube with a #2 pencil. take that tube out and now put a tubein the second channel socket and do the same.

THis answers a couple questions: What channel squeals or do both channels squeal. Does the power section make any funky noises.

You have resistors that need changing too. most likely 100K plate resistors and the, Im going to assume here 220K mixing resistors comming off the phase inverter tube.

Electrolytics should be changed unless they were recently changed.

If you feel brave enough...with the chassis out of the box...plug the amp in and tap on the circuit card with a #2. and tap lightly on the plate resistors and mixing resistors. You should NOT hear the tapping. If you hear the tapping, you have parts to replace.

the_man_dan · #16 08-26-2010, 10:56 AM

Quote:

Originally Posted by __HM__

Any idea where I could take it? Im near cincinnati... I wouldnt know where to start.. lol.

in cincinnati.. take it to chrome dome audio in sharonville.

BassmanPaul · #17 08-26-2010, 11:03 AM

the way that people are advised to open up a unit with potentially lethal voltages inside scares the hell out of me. No one should open a tube amp unless they know EXACTLY what they are doing. Sorry Mike, brave enough should have read foolhardy enough.

Take the amp to a tech - his bill will be far less that your life is worth!!!!

Paul

__HM__ · #18 08-30-2010, 07:22 PM

If I take it to Chrome Dome, or some other tech, what kind of bill am I looking at? I'm only 17, and by no means am I made of money.. lol. Thanks for all the help thus far.

__HM__ · #19 08-31-2010, 07:01 PM

Sweet, Adam at CD says it's $40 minimum, and that it won't be much more than that, judging by how I described the problem.

Thanks for the tips, all!

Tusec · #20 09-02-2010, 06:10 PM

Definitely interested in hearing what the problem turns out to be..