Fender ProTube Twin-Amp reverb feedback

[Mick]

Right, the 12at7 normally is used as the reverb driver and if this one's microphonic it feedbacks when you push it. You already did swap the AT7 as you said in the first post?

Yes, I swapped it with the original tube that came with the amp--a Groove Tube 12AT7. It didn't fix the problem. In fact, it might have made it worse.

One Thing you could check: Sometimes the reverb tank ist attached via 2 small round plugs, a red and a black one here they are called cinch-cable.
Check if there's a marker to show where the red one has to be plugged in - fender doesnt mark this, but a tech sould do that before unplugging when he takes the amp out - maybe someone didn't take care and swapped the two cables - I'm not shure what the effect would be but this could be it.

The cable from the reverb tank looks like a normal RCA cable. It has two wires and the connectors on the ends are color-coded (red & white). They plug into color-coded sockets on the chassis. I verified that the colors matched when I cleaned the connectors and sockets with the spray contact cleaner.

I hope we can help you - but here's another address you could contact: http://www.thevintagesound.com/ffg/

Greetings from Germany

Thanks! Hello from Deer Island, Oregon USA!