[tbone]

I think we can rule out the antenna coil secondary windings based on the AVC voltage being the same at all taps. I’m assuming it’s the same at the 6A8 cap which is important.

To me the AVC voltage dropout to the -2.6V level does indicate an issue in the RF section, front end and IF stage of the set.

If the stations still come in on the correct dial location, but just weak, I would also think the oscillator is good. I believe this was verified already.

If you can put your finger on the 6A8 grid cap and signals drastically improve as it previously did, then your problem is still likely between the antenna connection and the 6A8. You should be able to put your finger on the A terminal with nothing else hooked up and hear signals better than with nothing.

I understand that the IF signal passes through loud and clear, but there are too many variables to just say the IF chain is good. Not sure where the signal is being injected and at what level? You should be able adjust the level low enough to just be heard like you would do when performing an alignment. If the generator pumps too much signal, it can make you think everything is OK. Brute force.

If you can measure AVC as a reference when the radio is working vs not, while injecting the same IF frequency signal generator level, you would have confidence if the IF gain is stable. Maybe set it to get 4V AVC when the radio is good and see if it’s the same when the radios is weak.

Another puzzling thing is that even your strong transmitter fails to lower the AVC below the -2.6V reference. A strong signal should bleed through the radios front end and still be pretty good, hence my above IF stage comments.

I am curious as to whether or not the connected antenna is actually stable, and maybe the problem is not with the radio? You can connect up your signal generator to the A and G terminals on a broadcast frequency, not the IF, with a fixed level to see if the radio is stable or still drops out. This might be better than using over the air stations.

On a side note, I have seen tube sockets go intermittent. Sometimes the solder terminal looks solid, but the actual connection to the tube is bad. Also, wires soldered to grid caps can actually break inside the insulation and become intermittent.

All the advice you have been getting from Mike, Aaron, and MrFixer55 is spot on with troubleshooting. I’m simply thinking outside the box and throwing out some ideas that may or may not be beneficial.