Super Reverb reverb problem

[drewl]

I have a 65 Super Reverb reissue that the reverb will oscillate when turned up, the hotter the input signal the quicker it oscillates as the reverb control is turned up.
Sound familiar?
The reverb works, as you play you have reverb and as you turn the reverb up it will squeel...very high frequency, almost out of range.

The tank is good, send tube okay, return tube okay, cables okay, it's almost as if the recovery stage or possibly send stage are too hot...overdriving the heck out of the return stage.

So, what am I missing?
Voltages on send and return stages are good, reverb pot tracks fine, no opens..reverb is quiet until cranked and it squeels, and if you remove the send and return cables it will squeel a lower frequency when the reverb pot is at about 4 or so.

[txstrat]

Tubes?

[drewl]

No, tried new ones (a few) in the send and return stages.
The input impedance from the reverb recovery stage is ~200ohms from the reverb tank.
For now, I put a 330ohm resistor from the reverb return jack to ground and it kills the oscillation and there's still plenty of reverb.

It's weird, I could hit a chord on the guitar, let it ring, bring up the reverb control until it would oscillate, then that oscillation would be on the scope until I turned the reverb control down. So while I had the oscillation going i tried poking and probing around to see if anything would stop it....to no avail..

[TD_Madden]

Still think it's the 12AT7 (send)...I went through a few before I found one that wouldn't do tuat.

[52 Bill]

Try checking the filter cap for that power supply node.

[drewl]

Still think it's the 12AT7 (send)...I went through a few before I found one that wouldn't do tuat.

Still does it without the AT7 driver.
I did check all the filter caps in the doghouse, they seem okay, but that does make sense, and swapping another in is easy enough to try, thanks.

[drewl]

Try checking the filter cap for that power supply node.

Bingo! You are correct sir.
They used some cheap "Lelon" caps for the 3 22uf filters istead of the Illinois ones that they did use for the 2 100uf.
I checked em, but didn't see the spooge coming out of one.
I replaced all three and it's dead quiet with no reverb squeel.
What tipped me off is I had another one that was noticeably quieter.
Thanks for the tips.

[52 Bill]

Bingo! You are correct sir.
They used some cheap "Lelon" caps for the 3 22uf filters istead of the Illinois ones that they did use for the 2 100uf.

I've replaced some of those same caps on a Blues Deville or a Deluxe, I can't remember, but they seem to be really cheesy caps.

Glad you got it working.