[MrFixr55]

Dan, I'm at a loss here.

Turning the trimmer (compensator) screws CCW (Counterclockwise) lowers the capacitance because the distance between the plates increase. It is a little strange that they have Cap # 14 as part of Cap #7. It is possible that a shoulder washer between C14 and C7 would prevent squeezing the stack from changing the value of C14. Consider reassembly but not putting C14 in the circuit but replacing it with a fixed sealed cap.

I would consider replacing the 3500pF cap with the 2 caps that you have. The error would be about 3%, well within the 10-20% error allowed for radios of the time.

I suppose that the diagnosis would go 2 ways: First off, verify that your signal generator is accurate by checking against a radio with digital tuing. Your car radio would work fine if you don't have a portable or home radio that is digitally tuned. Next, determine if the RF section of tuning is accurate on this radio. this would be done by disconnecting the grid cap and connecting it to the antenna of another radio, tuning the other radio and signal generator to the same frequency and rotating the dial of the 38-10 that you are trying to repair to verify that the signal in the radio used to detect the signal generator peaks at the correct dial position on the radio under repair.

The final part is more difficult and that would be to verify that the oscillator section of the radio under test tracks at 470KHz above indicated frequency on the dial of the radio under test. I have to do some thinking on that if you don't have a frequency counter.

I don't think that the 20 Ohm resistor between cathode and ground makes much difference. Considering that the plate resistance of this tube is likely over 100KOhms, the 20 Ohm resistor is a drop in the bucket. I don 't know what the advantage of having that resistor in the cathode circuit is, given the total tube cathode to plate resistance. The EEs in our gang here may have a better explanation.