Amp problem

[scotto]

Late 60's modded Bandmaster suddenly turned into a tone generator that sounds like the synth in Emerson Lake and Palmer's "lucky man." It's a continuous tone that stayed after unplugging the guitar. I let it cool down so I could swap some tubes out but wondered if heat had something to do with it. Turned it back on with same tubes and it's no longer acting like a synth. Anyone experienced this before?

[Cliff Schecht]

Your electrolytics could be dying. When the amp is on and cooking, the heat from the tubes heats up the caps. This combined with the internal esr of the old caps trying to suppress the ripple voltage causes even more heat and quickly sends bad caps into thermal runaway. When the caps get too hot the esr shoots through the roof and regulation goes to crap and the amp turns into a howling mess. Once the amp rests and everything cools down, the esr is low again and the caps can do their job.

Just a thought..

[scotto]

Thanks Cliff!

[selloutrr]

this might help

http://www.geofex.com/ampdbug/squeal.htm