The roaring silence...

[not brand x]

Greetings Everybody!

I have an '84 Peavey Classic VTX 65 watt with two 12" speakers. It had been in a friends garage and when I turned on the power, the hum started as the tubes warmed up. Everything seemed to work correctly, just the hum. The other night while playing the hum suddenly became louder until turning into a full-blown roar. I killed the power and the roar stopped. With power back on the roar became louder as the tubes warmed. I turned down all the pots and when turning up each, one at a time, the roar is coming from the norm gain pot. I've searched the archives yet can't seem to find a post that covers my problem. Would anybody here know what might be troubling my amp...?

as ever,
not brand x

[Enzo]

OK, turn up the NORMAL control and get noise. Turn that control down, turn up the pre and post controls and play the amp through the lead channel. Does that work OK?

If the amp works OK through the other channel and ONLY the normal channel has the noise, then my first suspect would be a bad 4558 op amp IC at U1. That is the 8-leg IC nearest the input jacks, right behind the pre and saturation controls. Should be in a socket. Obviously ther are other possibilities.