On Mon, 30 Dec 2019 06:52:40 -0800 (PST), "
wrote:

Is it a mono or stereo amp? If stereo, is the noise identical in both channels? Can you hear suspicious noises coming directly from the electronics (like crackling from the transformers)? In the absence of any diagnostic linformation, my knee-jerk reflex is to suspect the coupling condensers, followed by the cathode bypass and power supply filters. When you have the noise, try freezing one component at a time using freon spray. If you have an oscilloscope, does the noise show up on the power supply b+? These things do not have very many components, and you ought to be able to divide and conquer.
The amp is stereo. The noise is coming from one side only. I'll post
more info in another post.
Thanks,
Eric