squealing reverb in a Supro Corsica

[matteee]

Hey all,

First time here. Looks like a great resource.

I just got a '66 Supro Corsica off ebay. It's a single 6v6, a rectifier tube, and 4 12AX7. Sounds great except that the reverb squeals like a banshee when I turn it on. The seller said it worked fine, and I trust him on that, but what's up? I tried changing the tube (1 12AX7) and that didn't help. Could something have happened in shipping? It was professionally packed, very well done, but who knows. The only possible clue is that the part of the tube socket that holds the shielded tube retainer, the thingy with the little nubs that the retainer screws on to, is missing on that socket only.

Any help is appreciated. Thanks in advance.

[52 Bill]

Welcome to the place.

By squealing do you mean that as you rotate the reverb control there is a squeal that comes up with the control or does it start slowly and build up to a squeal?

It could be anything causing the squeal, but I would think that the tube shield is not the problem. Some things to check would be the cable that connects the reverb tank to the amplifier circuitry. Dirty or oxidized tube sockets. The Reverb tank itself, for loose or broken wires.

[matteee]

Thanks Bill. I'll be more specific. Turn the verb up past 2 and there's a very loud piecing feedback. Not gradual at all.

[52 Bill]

Does the reverb work before the squeal? If you shake the tank, does it make sound through the speaker?

[matteee]

The reverb seems to work a little. I just checked it after putting the tube back in and now I can turn it up to about 7 without the feedback. Weird. It's a pretty weak reverb, but it seems to be there. The reverb knob seems at this point to function more like a presence knob, adding brightness, noise and drive as it's turned up. When I tapped the reverb tank I got a sharp click, not the sustained springy racket you'd normally expect. The connection to the tank seems fine. Maybe it's the tank?

[greekie]

Is the tank connected the right way? I once tried this when the input was connected to the amps input, and vice versa.

Other than that, if the reverb it activated with a foot switch like in the Fenders, it could be the cable - try to unplug that switch and see if it goes away. I was about to go insane figuring out a problem on my old SuperReverb, when I realised it was the footswitch cable that introduced noise into the circuit.

Jake