Peavey Musician III Reverb too strong

[Axtman]

A while ago I replaced the reverb tank (MOD 4EB2C1B) in a Peavey Musician III amplifier. Today while playing the amp I notice the reverb is really strong. If I turn up the reverb knob the amp start feeding back. It feeds back like sympathetic vibration feedback similar to resting a guitar on an amp that it on. The feedback is NOT an electronic squeal sound. The reverb just keeps going and going. When I turn the reverb knob all the way down (off) there is still a bit of reverb. In fact there is reverb even when I plug the guitar into the non reverb Channel A.

Any ideas would be appreciated. Thanks.

[Mick Bailey]

Can you post a schematic? I take it the old reverb was OK when it was working.

[Axtman]

Mick,
When I got the amp the reverb tank was broken. So I bought an replacement with the exact model number. I will post the schematic but I am now thinking that the "feedback" is mechanical and not electrical in nature. I am going to pull the reverb tank out and set it away from the amp and see if there are any issues.

Musician MK III.pdf

[Enzo]

First, is the reverb pan screwed down tight? I needs to float. The screws should be through the rubber grommets just enough to keep the pan from moving around the cab.

Is the pan inside a vinyl reverb bag?

Is the open side covered with a piece of cardboard cut to fit and taped in place?

[Axtman]

The reverb pan is screwed to the top of the amp head cabinet. There is no cardboard or bag that is typical when the pan is at the bottom of the amp cabinet.

I loosened the pan mounting screws a bit and it helps reduce the "feedback" a bit. I am going to experiment with different gasket material to help dampen the pan. The pan sure is sensitive. Slight tapping on the top of the amp will be heard.

I don't know if this makes a big difference but the original reverb tank was 4EB2C1A which is for a horizontal mounting open side up. I installed a 4EB2C1B which is for a horizontal mounting open side down.

[g1]

Is it the stock speaker? Sometimes a non-stock speaker with a bigger magnet can cause this.
Your idea about horizontal up or down is also feasible. You can try adjusting the springs that mount the inner pan to the outer chassis via the multiple holes where the suspension springs meet the outer tank chassis.

[Enzo]

Did you pull the reverb pan? Inside is the subassembly for the long springs. It is suspended by four short springs at the corners within the larger pan. Sometimes a small spring comes loose and the pan innards rest against the pan wall, causing this sort of sensitivity. Also there is usually a post sticking up through a hole in the innards, and sometimes the innards hops up on top of that post. Check for those.

Do cut a hunk of cardboard and tape it over the open side, it helps.

Does it help to grasp the pan with your fingers to reduce resonance in the metal box of it? A trick there is to stick a strip of self-adhesive foam waetherstripping down the center of the pan top.

[Enzo]

That would be a mighty big speaker magnet as the Musician is a head.

https://assets.peavey.com/literature...IIMusician.pdf

[Axtman]

"When all else fails, read the instructions!"

Okay so I solved one of the problems. The reverb is supposed to be on BOTH channels! Silly me for thinking it was only on Channel B.

I think I know what the problem is for the reverb feekback hum and sensitivity. It seems that it does matter how to mount the reverb tank. I bought a reverb tank that is supposed to be mounted open side down but I am mounting it open side up. I removed the reverb tank and notice that the inner aluminum channel rests on the top (bottom) of the tank. I moved the 4 springs holding the channel and it gave it a bit stiffer tension so that channel does not bottom out. I also removed the 4 brass rivets from the gasket feet on the pan. That will give the tank a bit more cushion. I will keep you posted.