[LASJayhawk]

I assume your model 90 has 1 #47 output tube by the volume control works comment.

My best guess is that the radio is our of alignment, if the antenna coil tuning isn't tracking the oscillator it attenuates the signal (the radio is trying to receive say 900 but the front end is tuned to say 870) if the if coils are tuned to the wrong frequency the same thing will happen.