[MrFixr55]

Hi Mike,

Make sure of a couple of things:

If you have another battery TRF set, test the tubes in that set.

Make sure that the 2 transformers in the 3 Tube TA are not coupling to each other. They need to be placed "orthogonally". Having one standing up and the other laying down should help. This is what they did in the transformer can of the RCA Radiola 16, 17, 18, etc.

Run the set with only the 2 AF tubes. There should be no "whistle" no matter how high you turn up the filament resistors.

Add the detector tube. Touch a wire to the condenser / secondary coil input to the detector TA (Left hand side terminal closest to the detector tube, marked "In"), and try to tune in a station with the rightmost tuning cap. If there is a strong station nearby, you should get it. At least, you should not get the whistle

Add the 2nd RF amp and touch a wire to the grid terminal of that tube. Try to tune using the center and right condensers. You should get a station.

Finally, add the first RF Amp and repeat.

The AK20 had 1K wirewound resistors between the grid of each stage and the junction between the stator of the cap and the "high" side of the secondary of the RF transformer. Both A-K and RCA had problems with TRF sets oscillating. Also remember that these sets are not neutralized.

If the set oscillates when adding a tube, swap out that tube.

You can also "signal inject" to check out the radio. Use a transformer between the signal (CD Player, etc.) and the stage that you are injecting into. If injecting into the grid of the 1st audio amp, you should hear the audio that you are injecting. You will also hear a signal if you inject it directly (through the transformer) to the grid of the detector