(06-30-2016, 09:06 AM)Steve Davis Wrote: [ -> ]Next, place another radio next to the radio under test to see if you can tune the local oscillator of the nonworking radio.
Steve
I think I already know the answer to this but do I need to use another antique radio or will a modern portable work? I would think a modern portable would be fine.
Answer is yes. Put it near the 6a7. Set it's dial at 1000kc. tune the Philco to 1460kc and if all is well you'll hear a hiiss in the portable. Tune the Philco a bit as it may be a little off in frequency.
Terry
I tested the voltages on the 6A7 on all 4 bands to see if the band switch had any issues. Got the same voltages regardless of Band:
Hooked up a signal generator, red lead to grid cap of 6A7 (cap removed), black lead to chassis ground, 460 KHz. I did hear the tone at the speaker loud and clear.
Next I tried putting a second radio next to it, but first I tried it on a working set to know what to listen for. Used my Zenith 9-S-262 set to 1000 and used my TransOceanic B600 and was able to hear the quiet spot around 1460. I verified it was the quiet spot by turning off the 9-S-262 and the regular background noise returned on the B600. I also adjusted the dial back and forth on the 9-S-262 around 1000 and the quiet spot would fade in and out on the B600. Tried it on the Philco 640 and could not hear a quiet spot.
Finally figured out where I went wrong. I mis-read resistor #50. It is supposed to be 25K and I had 250K. Also, I had resistor #51 in parallel with #41. It should have connected from #50 to capacitor #54. Works fine now.