Strange squeaking noise

[Ptron]

I'm trying to fix a bandmate's Silvertone 1465 185.12011 amp that will ocassionally, spontaneously start making a noise sort of like rubbing a balloon really hard: a hard, squeaky sound with bending pitches. The amp was found in an abandoned building and currently lives in a damp basement.

My first guess is it's arcing, maybe in a cap. I don't really know what to do other than shotgun replace an assload of caps so I thought I'd ask here for any advice y'all might have. Are resistors prone to this? It's got a bunch of cement wirewound ones. It's got a transformer driver "PI" I suppose that could arc too.

[Enzo]

If anything is arcing, it is much more likely a tube socket or a transformer. And frankly, first thing I'd do would be try a different set of tubes in it.

Gently push on each wire from the PI trans to see if any are broken.

Do any controls affect the noise IN ANY WAY?

[Ptron]

Thanks for the reply enzo. This one is SS. It does strangely enough have a transformer "driver/splitter/PI" . I'm not sure what to call it.

I haven't had a chance to see if the controls affect the noise yet, the amp can go a long time without making it. I'm not even sure it will do it in the relatively dry conditions I have it in now. I'm going to leave it on for a while and maybe I'll get lucky.

[Ptron]

Well I just heard it for a second when I turned it on but it died down before I could mess with anything.

I should probably mention that I've thoroughly chopsticked the amp and haven't been able to make it happen. I should also mention that it works just fine otherwise.

There is a cement resitor whose glue caps have come off and you can spin the cement body around, but that doesn't make a noise. Also, a whole bunch of the small e-lytics have what looks like a ring of orange rubber that's pushed out of the + side. Comparing to the ones that aren't doing this, it looks like this rubber is part of the construction and has just expanded out on some of them. Maybe I'll post a picture.

[Ptron]

OK, new info...

First...I realize my discription of the noise as a squeak may be a bit misleading as it isn't high pitched. It's more of a creak. Maybe think of a theramin, like in Whole Lotta Love. That said....

...I just turned the amp on and it was making plenty of noise... only it was more of your garden variety sputtering & static. (It sounds like the creaking sound may just be the sputtering when it really takes off.) This time I had plenty of time to mess with the controls and poke around with a chopstick, none of which affected the noise.

The noise eventually died down, so twice it's happened when I powered on, then gone away. Something, warming up and drying out maybe? In the damp basement where we play, I'm used to the noise popping up suddenly after the amp has been on for a couple of hours.

[Don Moose]

The big cement block is supposed to be a heatsink for the resistive element, and if the block spins, it could let moisture in, which could futz with the impedance ... maybe. In any case, I'd call that part damaged and put it near the top of the 'replace now' list.

The electrolytics - they're axial (a pin out each end)?
- they're built like a kind of cup (the negative electrode is welded to the metal body of the cap?
- With the amp on, do the ringed caps feel warmer to the finger than the non-ringed ones?

That says to me that:
- That orange rubber thing is either the seal or the electrolyte pushing out due to ?heat/mositure/age? If you have a suitable cap-meter, yank one and test it.

Hope this helps!

[Arthur B.]

Thanks for the reply enzo. This one is SS. It does strangely enough have a transformer "driver/splitter/PI" . I'm not sure what to call it.

They're called interstage transformers.