Hello Dave,
I am not familiar with the set, but having said that, maybe the first suspect should be the oscillator. You say the voltages are correct. There should have been a negative voltage measured on the oscillator tube, and it would be helpful to measure that ASAP, right after the set dies, in the "three minute" window. No neg volts...no oscillator. If that's the case, then try a new tube. Often "good tubes" are marginal in some oscillators. When oscillator troubles develop they usually show up on the higher frequencies first (like shortwave). But why your shortwave bands work OK on their higher ends, but not the lower ends is odd. I am sure others can add to this. Good luck.
Jim |
Dave Froehlich 