[MrFixr55]

Hi SQ55,
A strange issue indeed!  Just so I have you straight, on a dim bulb you get normal operation after the set warms up.  Do you get hum before it warms up when on the dim bulb?? Did you use correct "working voltage(WV) on the electrolytic caps? Consider using a minimum of 350 WV for C101. 400 or 450V may be better. the reason for this is that the 'no load' voltage on C101 (for example, if the set was powered up without the speaker plugged in) could be much higher than 350V. If the set was, in fact, powered up without the speaker plugged in, that cap may be damaged. C102 A and B should be 300 or 350 WV.

I am not surprised that you have AC on pin 3 of the 7AF7 when the radio is playing, along with the hum.  The plate of an audio tube has both an AC and DC component when it is amplifying an audio signal. In the case of this stage, there would be an AC component on the cathode of the invertor stage also. The schematic states that voltage readings are taken with the volume control at minimum. In a good set with no hum, there would be little AC superimposed on the DC readings on the pates and cathodes in the audio stages.

The 7AF7 tube has 2 triode sections.  One triode is the phono preamp, only used for the phono.  The other triode, the one that we are interested in, is used as a "cathodyne" phase invertor and provides signals to the grids of the 2 6V6 output tubes.  Because these 6V6s are a "push-pull output stage, the signals feeding one 6V6 must be 180 degrees out of phase with the signal feeding the other 6V6. One 6V6 grid is fed from the plate.  The other 6V6 grid is fed from the cathode.  The signal from the cathode is in sync with the signal going to the Phase Invertor grid.  The signal from the plate is 180 degrees out of phase.  You can expect both an AC and DC component on the plate and cathode of this phase invertor if there is audio or a hum.

Does the hum coincide with the volume control's position?  What happens if you leave the 7AF7 in but pull the 7X7 Detector / 1st Audio Amp.  If the hum disappears with the 7AF7 in but the 7X7 out, then the hum is coming from that stage (1st AF) or before that stage.  If the hum remains the same, then the issue is with the phase invertor. It is possible that there is leakage between the filament (heater) and the cathode.  If the convertor is also a 7AF7 then swap the tubes and see what happens.  If the convertor is a 7F8, then you will need to find another 7AF7.

You should also check both DCV and ACV on the power supply with and without the 7AF7 in place.  At the junction of C102A and the speaker field, the AC "Ripple" should be less than 2V.

Hope this helps. Keep us posted nd good luck!