Amp Screeching, Voltage leak?

[Christopherrgerhardt]

On a friend's Peavey-Musician, Series-400 bass head; at any volume other than the lowest low I get a high-pitched ring that increases with either gain or volume. I want to make it clear right now that this is not feedback. Sounds similar to some voltage leaks I've heard in the past where a bad electrolytic was leaking DC into the ground. Problem is, I can't find it. I don't have a capacitance meter and am without a scheme to see what values are supposed to be present in some of the worn down components.

The amp is solid state and high wattage with HUGE filter-caps, so I want to see if any-one has had this issue before before I blow up another cap-drain, lol

The two pics are of the amp itself to maybe jog a memory and of a component in the power-amp, RIGHT before the output, that i"m having trouble identifying. it's in pretty bad shape and if it's a choke I bet it's the culprit.

[Jazz P Bass]

The coil is a part of the Zobel Network.
Highly unlikely that is the cause.
I have attached the 400BH schematic.
Check all of the power voltages for stability & low ripple voltage.
High Vac ripple will indicate a bad capacitor.
I think this amp has a Boost Output.
See if the screaching is on that socket. (scope, DMM, Run it to another amp.)
That should you isolate the problem to the pre or power amp.
If the Boost out is o/k, than you have a power amp problem.
I do not have the preamp schematic.
Might want to give Peavey a call if you need it.

[Gtr_tech]

Its oscillating. With any amp of that age you will prob'ly find interstage coupling caps that are beyond their useful life. They're small and cheap, so it'd be a good place to start by just replacing all the electrolytic caps in the front end.