Whats the deal with an amp that squeals?

[jerryjg]

Ive got a '69 Sunn S2000 tube amp thats squeals like a mofo. I cant get anywhere near it with a Strat. None of my other tube amps exhibit this problem when cranked. I thought it was only pickups that squeal, but evidently amps squeal also. Anyway, its freshly serviced. Could it be a tube??

 

[Rich_T]

Re: Whats the deal with an amp that squeals?

High squeals are very often a sign of bad tubes.

 

[lastwinj]

Re: Whats the deal with an amp that squeals?

hard to etermine the cause without being there. strats are notoriously loud in most amps, noise wise.
my guess would be the amp needs to be shielded more.

germ

 

[Low_fidelity2100]

Re: Whats the deal with an amp that squeals?

I'd say its most likely a microphonic preamp tube. Does it only happen if the amp is turned up past a certain point? or does it happen even at low volumes? Does it happen with other guitars, or just that strat?


Anyways, best way (afaik) to find a microphonic preamp tube is...
1. With the amp off, remove any preamp tube covers. (I dunno whether yer sunn even has those.)
2. Turn the amp on set to your normal volume. Let it warm up, then switch it off of standby.
3. With a guitar plugged into the amp (or even just a cord). Go behind the amp, and tap lightly on each preamp tube, listening for noises. (a chopstick or wooden part of a pencil works well)
4. If tapping on one of the preamp tubes causes the amp to start squeeling, then you've found your bad tube.
5. Replace that tube (or swap it with another tube in the amp where microphonics aren't a big deal), and if that solves the problem then yer done.

Now sometimes tapping on the tube won't actually cause it to start squeeling. You might just hear a ringing chime sorta sound, or a long sustained "ding" that slowly fades out. Whatever the noise, if its really noticable, and seems to "ring". Thats most likely your bad preamp tube.
It'll most likely be in the first two preamp tubes (furthest away from the power amp tubes). But it might be in any of them. I had a set of 6L6's once that would squeel and become microphonic at high volume, before that I never even knew Output tubes could be microphonic. So ya may check that too, if none of yer preamp tubes are bad.
A little noise is to be expected in the first 2 preamp tubes of most amps, if you tap on them. Even a totally fine tube when tapped on will make a "clunk" sorta noise. So don't worry about that, what your looking for is a sound that rings out for a few seconds, or a chimeyness.

Also if you have those spring retainers on your output tubes (the kind with the little metal cup that fits over the top of the tube, and springs that attach to the chassis to hold the tube in the socket). Sometimes at high volume the springs will get a sympathetic vibration going that will cause the Output tubes to vibrate. Which can come off as a squeeling.

Lastly, I don't know if that amp has reverb or not. So this might not be even a possible issue. But I used to have a crate Vintage club amp where the Reverb pan would get microphonic and squeel if I had the verb above 3, and the amp volume above 5. I've never had that happen with any other amp though. So I dunno. I'de say check that last if you can't find any problem with the tubes.

 

[kmcguitars]

Re: Whats the deal with an amp that squeals?

Freshly serviced? By who? And what was done? There are a number of things that could cause squeals, This is why I ask what was done to the amp, And was the tech repable/knowledgeable? (Does the amp squeal w/t Humbuckers and quality potted single coils?) If Yes is the answer. Take it back to your tech or find a better Tech. My shot in the dark would be the filter caps. Have they been replaced?

 

[disturb]

Re: Whats the deal with an amp that squeals?

If it's not a preamp tube, it could be the power tubes. I have an EL34 amp that produces a lot of bass. When the head was on a 4x12, the huge bass vibrations caused the filaments in the EL34's to vibrate, and it would squeel. When I took the head off the cab and sat it on the floor, the squeeling stopped. I since replaced the tubes with sturdier EL34's, and now can have it on the cab again. Whenever I can, when buying tubes, I put them up to my ear and shake them. If I hear excess rattle, I pick another one. Anyway, after you check your preamp tubes, set the head on the floor while playing and see if it stops. If so, you found your problem.