reverb feedback

[Christopher30]

got a tube amp, just had the tubes replaced about a month ago, and now it hums with this high pitched feedback when the reverb volume is turned up at all. Any ideas?

[Enzo]

Yeah, your reverb pan is feeding back.

Is it screwed down tight to the cab floor? SHould NOT be. A couple screws to just keep it from sliding around.

Is it in a reverb pan vinyl bag? SHOULD be.

Is there a piece of cardboard cut to size of bottom of pan, and covering it? SHOULD be.

Aer all the long springs inside it intact? SHOULD be.

Are any of the four small springs at the corners that support the innards come free? Should NOT be.

Take the mounting screws out and move the thing around. Sometimes as little as an inch or so will find a less sensitive spot where the standing waves don't form.

SOmetimes flipping the whol;e thing over on its back works. This for the ones in a bag, which yours should be.

And sometimes you just have to get a new reverb pan.

Your pan will have a long number on it like 4AB2C1B or 9EB2C1B or something. That is the pan type. A reasonable place to buy them is www.tubesandmore.com

[Mars Amp Repair]

Agreed,
also a bad or corroded ground connection on the output rca plug to the pan or to the amp can cause mucho squealing, too. glen

[Enzo]

Actually now that you mention it, that sounds more like his description.

[keithb7]

I know this is an old thread, but I thought I would add my findings here so others may learn. I searched Reverb+Feedback and this thread came up.
I am working on a 2012 Fender 65 Deluxe Reverb re-issue amp. Howling feedback as reverb knob is turned up. Made no difference if tank was mounted
in amp cab or out. I pulled chassis and reverb tank and placed them on my bench. Tank was nowhere near chassis. Still howling. Upon further inspection
I found that somehow the inner tray that support the springs was dislodged somehow from its home. There are pins, and the inner tray has a holes in it, with a
rubber grommet around it. The inner tray was somehow bumped out of it's floating position and pushed against the outer tray cover, no longer free floating.
I put it back into place and all reverb problems are solved.

Sorry it I awoke a Zombie thread. Just thought it might be an appropriate place to comment. Regards, Keith.

[pdf64]

Back to post #1, if the amp uses a shared cathode for cascaded stages, as per V4 of BF / SF twin channel reverb amps, then a bad cathode bypass cap can cause this issue, ie howl type oscillation as reverb intensity control is advanced.