[radiomikee]

I had one like this recently. Turned out, I had a broken wire hidden in the insulation to the plates of the RF Amp tube one stage earlier than the mixer tube. Tapping the radio, or changing bands sometimes got the wire ends touching, so it would play, but stop again quickly. After replacing that wire, perfection. I might try checking the pin voltages to the tubes ahead of the 77, and see if a wiggle here or there upsets things or corrects it. The point to point solid wire in these sets is pretty thin, and sometimes a little nick from the wire stripper creates a weak point where it later cracks.