Vox Super Beatle Reverb issue

[Caesonia]

Hi all!
My Vox Super Beatle head has a good reverb tank, but it's developed a problem lately: no matter how low the volume is, if the reverb is turned up above 2 or so, it starts up a feedback howl. This seems to happen even if I'm plugged into a different channel where the reverb isn't in use. Does anyone know why this might be the case? Thank you.

[phatt]

Check the RCA cables going to the tank, they can get corrosion over time.
Also the tank is normally rubber mounted and they can rot.
If the tank is not mechanically isolated from the cabinet (or case) well, that can cause feedback.
Phil.

[Caesonia]

Thank you Phil! I'll check those connections and see if I can find the problem.

[g1]

Also, has the distance between the speakers and the reverb tank changed?  Like the tank moving closer to the speakers, or different speakers installed?
If cleaning the connections doesn't help, try moving the tank outside the cabinet (if the cables are long enough).

[J M Fahey]

+1 on the tank mounting.

Cabinet vibration shakes tank and causes feedback so manufacturers diminish that by "floating" it.
Minimum is using soft rubber grommets in mounting holes and NOT tightening screws, so tank has a little "play".

But rubber hardens, crystalizes and rots, plus some times eager owners tighten screws > instant feedback.
Fender even used a separate padded Tolex pouch to hold the tank, very loosely mounted.