The PHILCO Phorum

I just purchased a Philco 84B. It plays and tunes well. After 10 minutes, it will not tune and makes a high pitch squeal as the tuner is adjusted. Is this a part overheatingand what part might it be?

Thanks for any assistance.

Hard to say which part is at fault. I would poke around the detector circuit. Have any of the caps or resistors been replaced? Have a look at the 1 meg screen resistor and it's bypass cap. Also switch the 77 tubes.
Terry