05-20-2016, 12:18 PM
Sorry I may have misunderstood your question. I was thinking that it was a hum troublemaker but perhaps it is no signal problem. If this the case then using a signal generator to inject a signal it various stage to determine weather the stage is doing what it is spouses to be doing. With out that checking plate, screen grid, and cathode voltages is the next best thing.
Terry
Terry