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Valve Amp Problem, it goes QUIET.. then LOUD.. then QUIET.. :[


monto

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hey all, i was wondering if anyone had some basic idea as to what might be the cause of the problem below (the amp is a LANEY VC50 - 6 input valves 2 output valves)

 

"The amp works fine for a while (usually between 2-10mins) though it can be less or more (i presume this is the time it takes to warm up), and then it goes REALLY quiet, then back to normal, then REALLY quiet, it does this on ALL channels on all of the settings. It doesnt go loud and quiet in a regular pattern, its more just random (usually around 10-30sec intervals)"

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I've had this problem and it was just a fried preamp tube. Output tubes can cause this problem as well. You can swap out tubes and when the problem goes away...you've found the culprit.

I've been told by techs that if you keep operating the amp like this, you can eventually burn out your filter caps, which I can only assume is an expensive job.

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First test your power tubes, if any are weak or bad replace them. Or you could just replace them all with new. If that doesn't fix the problem it may be a bad filter cap, I had a simiular problem with one of my Fender amps a while back, everything else tested okay, and it still did it. So I replaced the filter caps and that fixed the problem. Another small possibility is in the rectifier circuit. I don't know your amp to tell much about that.

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