My Model 635 Philco gives a loud squeal when I turn the tone control and sometimes will do it when I turn the volume control up. After two or three minutes of warmup time the volume control doesn't make it squeal but turning the tone control to a different position always makes it squeel. What could cause this. I have cleaned the tone control contacts, recapped the set (90%) and put the electrolytic grounds where they were originally.

If you put the radio in the Phono mode. Does it squeal then ? If it does the problem is going to be in the audio stage. Post again.