[Boatanchors] Sentnel Radio Co. Musicair Console, Help Needed

[Ronald Doering]

I am in the process of restoring a Musicair Console Radio.  Replaed several defective capacitors.
The radio plays now, but after warming up for 2-3 minutes, it fades out, no audio.

Turn it off, let it rest a few minutes and turn it on.  It plays and then does the same thing again.

Anyone have some advice on what to check?  Can a coupling capacitor do this?  AGC tube?
Or, is it a tube?  All the tubes check out fine on a tube tester.  Something warms up and changes.
Any help will be appreciated.  Thanks,  Ron  100% DisAmerVet