Reverb feeding back

[Fiat_cc]

Hi all.
I built a Vox AC30 style circuit with the one tube reverb circuit that is somewhere on this forum.
I’ve used that circuit before and it worked great.
I’m this amp, it works a little too well, and it starts to feedback. Usually at a very ow frequency, although sometimes it’s higher. It’s in the same combo cabinet design I’ve used before, with a similar powered output section, but it definitely seems to be the tank feeding back. I’ve tried a different tank, playing with the orientation of the tank etc, but I haven’t stopped it yet. Lifting the tank and isolating it from the cab seems to work though.
Has anybody else had this issue and found a solid fix? Everything else about the amp is stellar.

[tubenit]

Is the reverb tank inside a bag to isolate it from the speaker?  I've also used outdoor carpet over a reverb tank successfully.

And I use rubber washers underneath the rim of the reverb tank. If you don't have rubber washers,  double stick tape will work reasonably well also.

With respect, Tubenit

[Fiat_cc]

Is the reverb tank inside a bag to isolate it from the speaker?  I've also used outdoor carpet over a reverb tank successfully.

And I use rubber washers underneath the rim of the reverb tank. If you don't have rubber washers,  double stick tape will work reasonably well also.

With respect, Tubenit

I’ve tried in and out of the bag. I’ve got some rubber grommets I’ll try under the tank.

[Fiat_cc]

I’ve tried a bunch of stuff now, and I can’t kill it. I’m wondering if it’s actually an oscillation in  the reverb section electronics rather than the tank itself. It’s hard to tell.
Once it starts though, the tank is vibrating viciously, but I’ve tried two tanks now with the same result. Even put a 12ay7 in to try and reduce the gain.

[sluckey]

Once it starts though, the tank is vibrating viciously,

While it's squealing unplug the send cable at the amp. Does it stop?