Weird reverb problems in tank? I'm baffled

[davemoog]

I just bought up an old Pioneer SR101 reverb. Although not strictly a guitar amp, this unit is often used with guitars or keyboards. When working it sounds OK for reverb (stereo) and also overdrives nicely. As for why I am posting here is that there seem to be so many forum users with serious knowledge of tube amplifiers and reverbs. The schematic can be found at http://www.angelfire.com/ky3/craigor...chematics.html

The unit is having a strange problem where one channel has way more reverb than the other. I've switched tubes around, checked levels driven into the reverb tanks and the signals going in are the same. The gain and amplification of the recovery amplifiers is the same.

I've swapped tanks from one channel to another and the problem seems located in the actual reverb tank. The coils of both units measure the same resistance wise, the springs are centred the same inside the laminations - and still one tank is louder than the other. One can actually hear when you drive the tanks that one tank (the good one) makes more noise......So where is the problem? It's got me stumped. Is something wrong with the laminations in the drivers/pickups??

Can anyone shed any light on this problem? Where to continue looking?

Thanks
Dave
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[6267]

When you switch the tanks from side to side, the problem follows them? If so, I'd imagine it is the tanks, you can pick some of these up from any of accutronics' dealers. Otherwise (i.e. the problem stays when the tanks are moved) I'd blame the reverb drivers. If it's tube, you should replace the tube(s). Sometimes one side of a tube will weaken before the other. If there are seperate driver tubes for each channel, try swapping these too. Also, transformer-coupled tube drivers sometimes partially or totally destroy their transformers, especially the little paper open frame ones. I would suspect bad tube, bad tank, bad transformer in that order. I'm assuming you've already checked voltages to the driver circuit.