mini prob with a twin reverb

evolucian

I recently tried a second hand twin reverb and there was a tiny prob that stopped me from buying it. All I can do is explain what it "sounds like" happened. Thats why I'm here explaining it to you guys so's you can help me ?

Both channels work well, complete with customary terribly shitty drive that Fender works so hard for. As is also customary for Fender... the volume jumps in at 2... 1 does not exist even though its there. Big and bulky like a nice amp should be. It has wheels fit for an ollie to be pulled off comfortably.

The reverb itself is what bugs me... it creates a mini feedback sound that just schwings within itself like its on a constant loop. A terrible sound that will shrivel and shatter many a man's beloved nuts. More than that I cannot explain. Would something like this be easy to repair and, without hearing it, would you tech heads know what it is?

shaunf

I'm no expert, but if I were to hazard a guess, I'd say it's possibly a faulty tube.

lapdawg

shaunf wrote: I'm no expert, but if I were to hazard a guess, I'd say it's possibly a faulty tube.

Thats exactly what I thought. I have just bought a a bunch of '60's EI ECC83'w(Yugoslavian-made using Telefunken tooling). They are absolutely epic for about 4 minutes when I switch on & then the squeal starts & escalates as they warm up
If this is what you have then you have 2 options - find the culprit & replace it or if its an expensive tube you can try damper rings. These are heat resistant silicon O-rings that go around the tube. They may or may not work.
You can pick up these damper rings cheap-cheap on eBay with free shipping to boot. Mine are in the post.

evolucian

ok... the amp itself is fine. I played on it for a good 3 or 4 hours before switching the reverb on and it was cool. No funny sounds or nada. It's only when the reverb is going that the funny schwiiiiing starts.

AlanRatcliffe

I've had reverb tanks do this and it's usually a mechanical problem with the tank or the mounting - acoustic vibration basically.

As far as mounting goes - The tank should be in a reverb bag and a Twin usually has a layer of thin foam under it in the bag - which often perishes. You'll find a lot of guys put a layer or two of cardboard under the tank in the bag to replace it. If the tank has any rubber mounting grommets, check them for decay too. Some stuff the bottom of the amp with all kinds of things to minimise the problem.

Occasionally it can be a bigger mechanical problem with the tank itself - the bottom plate being loose or a spring coming loose and lying on the other spring, the springs getting caught on the vertical posts, etc. (used to get this with Peavey amps a lot).

Oh - and yes, you should check the 12AT7 (V3) valve as a matter of course. Just swap it out with another. If you don't have An AT7 handy, a 12AX7, 5751 or a 12AU7 will work in a pinch just to test.

evolucian

Thanks alan... much appreciated ?