RM50 master volume issue - need help

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Sven S.-M.

Jul 20, 2006
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Hi fellow tube amp lovers

I have a RM50 Silverface Combo which I haven't played for some years, but now I've started to play it again only to find out it has a volume problem of some kind. That bums me out. It's a nice amp, but rather useless as it is!

The trouble is that the volume level rises after a couple of minutes of fiddling, like if you kick in 15 or 20 dB boost pedal only without driving the tubes, and when this happens the master volume pot fails - on the amp, not the modules. It's the same whether I play channel 1 or 2 and regardless which modules are in the amp. I've also experienced the volume to drop significantly. But right now volume only rises unexpectedly.

What to look for? I have checked power tubes JJ 6L6 with very little wear, they're both good - bias 21-22 mV. Amp sounds pretty "normal", no crackling or weird noises or smells. It has never been pushed hard, only played at small club and bedroom levels.

What can cause this kind of volume issue you think?

The boost jack on the amp is designed to bypass the master, could be a dirty intermittent contact on the jack. Try exercising it with a plug.
This is likely either dirty send and return jacks on your effects loop, a dirty boost jack or a broken master volume pot on the front of the amp that will need to be replaced. Email me if you need any help.
I had the same exact issue with mine. It turned out to be the boost jack in the back making an intermittent contact. The simple fix was to plug in a quarter inch TRS cable to the jack at all times. That kept enough pressure on the post to keep contact. Never had another issue
Fast forward 9 years and here we are!
Just want to give some feedback on your kind helpful suggestions and you were right - It was the sockets on the back.
Took me a while to save up and get it to good tech. He replaced them all with some better sockets and now it works as it should.

Thanks again.