02-04-2026, 06:20 PM
MrFixr55
I replaced the tube socket for the 6A8 and the 6K7, and tied pin one of each tube to ground. Solved all of the instability issues!
Re-did the IF alignment at 470KHz as specified in the procedure.
I did the BC RF alignment.
Afterwards I checked the frequency of the osc against the dial and discovered that the difference frequency was 440 KHz from 580 to 1600 on the dail. Tracked good but 30KHz lower than spec!
The RF alignment was strange in that the effect of adjusting C7 and C9 were reversed! Is anyone aware of an issue with the documented locations for C7 & C9?
It is entirely possible that I accidently reversed them when I rebuilt the compensator, oops!
I re-aligned the IF to 440KHz and the radio receives stations at the correct location on the dial, however weak until I touch the grid cap of the 6A8 and WOW!!! So now the BC ANT coil is suspect. The primary of the BC ANT coil measures 0.082 ohms. I suppose there could be some shorts???
How many turns are on the primary, not too many I would guess.
I am going to chenk the coil by applying my RF generator to the antenna terminals and monitor the grid cap of the 6A8 with a scope to ensure there is good coupling and the signal peaks at the frequency set by the dial.
Grounding the set did not change much.
Not sure why the OSC tracks at 440KHz above the dial, most likely the range of capacitance on my rebuilt compensator caps are off a bit. I could adjust the values a bit. Or, a 440KHz IF is ok???
Am I on the right track?
Getting closer,
gpurtchick
I replaced the tube socket for the 6A8 and the 6K7, and tied pin one of each tube to ground. Solved all of the instability issues!
Re-did the IF alignment at 470KHz as specified in the procedure.
I did the BC RF alignment.
Afterwards I checked the frequency of the osc against the dial and discovered that the difference frequency was 440 KHz from 580 to 1600 on the dail. Tracked good but 30KHz lower than spec!
The RF alignment was strange in that the effect of adjusting C7 and C9 were reversed! Is anyone aware of an issue with the documented locations for C7 & C9?
It is entirely possible that I accidently reversed them when I rebuilt the compensator, oops!
I re-aligned the IF to 440KHz and the radio receives stations at the correct location on the dial, however weak until I touch the grid cap of the 6A8 and WOW!!! So now the BC ANT coil is suspect. The primary of the BC ANT coil measures 0.082 ohms. I suppose there could be some shorts???
How many turns are on the primary, not too many I would guess.
I am going to chenk the coil by applying my RF generator to the antenna terminals and monitor the grid cap of the 6A8 with a scope to ensure there is good coupling and the signal peaks at the frequency set by the dial.
Grounding the set did not change much.
Not sure why the OSC tracks at 440KHz above the dial, most likely the range of capacitance on my rebuilt compensator caps are off a bit. I could adjust the values a bit. Or, a 440KHz IF is ok???
Am I on the right track?
Getting closer,
gpurtchick




