[MrFixr55]

Hi DConant,

Stert by trying the grid cap of the 1st IF (with the grid wire in place; ground the ground lead of the generator; set the generator to the IF frequency). This does not check the 1st IF transformer secondary coil but may check the trimmer capacitor. You could connect to the 6A8 plate terminal through a capacitor (I'm guessing 0.001uF; remove the tube). That would validate the transformer. If the intermittent occurs, then the issue is in the IF, Detector or Audio stages. However, if you played an external input for a long time with no issues, the AF stage and most of the power supplt is good.

Next step would be to connect to the grid cap of the 6A8 directly (Disconnect the grid wire and connect the ground terminal of the test lead to the chassis). Set the tuning cap full open, set the generator to whatever frequency near 1630KHZ that is received.

Next, same connections but connect the grid wire also. If the first 2 steps are successful but the 3rd step causes issues, then the antenna coil may be at issue.

Finally connect across the antenna and ground terminals.

One other possibility:

Check the screen grid voltages on the 6A8 and 6K7 when this happens If too low, this will greatly lower the gain of these tubes. In fact, in very early "Screen Grid" radios (radios containing tetrode RF amps), varying screen grid voltage was a method of controlling volume, but adjusting cathode bias and shunting the antenna coil with the same pot was more popular.