Peavey 6505+ squeals

[Tech. Tom]

Hello:
The amp squeals when you use the lead channel.
If you turn the lead gain (pre control) past 6
if squeals at about 1KHZ, it sounds like a tone generator.

It does it with or without an input.

Hoping someone has had to deal with this problem
and can save me some troubleshooting time.

Thanks for any help.

[alexradium]

Try changing preamp tubes, then check filter caps

[Jazz P Bass]

I would pull V1 to see if it stops.

That is The Most Critical tube in the amp.

[Tech. Tom]

I would pull V1 to see if it stops.

That is The Most Critical tube in the amp.

I did remove V1 and the squeal stopped but when I subbed in a new tube it came back.
I also subbed in the other pre-amp tubes but still had the squeal.

I guess I'll have to check all components in that circuit for defects.

Thanks everyone for the input.

[Enzo]

That tells you that V1 is involved in the oscillation. Doesn't mean it is at fault, but it is involved.

Don't assume all problems a a "bad part". A poor ground connection could be the problem, such as a screw on the corner of the board that also serves to ground the circuit to the chassis, that sort of thing.

[Tech. Tom]

I didn't see any ground problems. I spoke with a Peavey technician and he said it might be a normal condition with the gain turned up that high, but it seems to me
that they wouldn't have engineered it that way.

[alexradium]

I didn't see any ground problems. I spoke with a Peavey technician and he said it might be a normal condition with the gain turned up that high, but it seems to me
that they wouldn't have engineered it that way.

it sounds like a positive feedback,due to a bad filter cap,either c35 or c72.
you can parallel a new one with clip wires,see if it changes