I have an old late 70s Peavey PA-400 powered mixer. It's a workhorse that suddenly started doing the following:As soon as you turn it on - both speakers hum pretty loudly, and the back of the PA begins to get really really hot. If you plug in a mic while the speakers are humming, PA overheats and auto-shuts off. After cooling, you can turn it back on.If I turn on the PA (without the speakers plugged in) and leave it on for a good 15 minutes, then plug in the speakers - no humming at all - no significat heat either.All seems to work well if I let the PA "warm up" for about 20 minutes! Something is definitely wrong.
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