I have recently finished refurbishing a 37-610T with new caps, etc and performed a complete alignment. When doing the alignment I noticed that the level of signal from my signal generator required to give similar voltmeter readings on the plate of the 6F6 output tube as for the SW bands was about 5-10 times higher. The osc. and antenna coils seemed to adjust properly but when receiving stations I get much stronger reception connecting the antenna wire to the grid of the 6A8 converter tube rather than to the antenna input strip.
I ohm'ed out the BC antenna coil and the readings are spot on for both primary and secondary and there is infinite (>10M) resistance between them. Could this coil have a shorted turn which would show a negligible difference in DC resistance but ruin RF coupling? Is there an easy way to check for a shorted turn other than removing the coil and examining it?
Thanks,
Steve D
If you want to test the antenna coil you would want to test the resistance of the primary and secondary. If either one or both are open(more than 1000 ohms) the coil should be repaired or replaced.
Terry
I states in the alignment instructions that the antenna link should be on terminals 2 and 3. Is this where it is?
Yes, The antenna is connected to terminal 1, and terminals 2 and 3 are linked together. I do not have a ground wire from the chassis to house ground. Do you think this will make a difference, and if so why just on BC and not on either SW bands?
Steve D
I did some further checking. With the RF gen. and the tuning dial set to 1.1Mhz I connected it to first the antenna terminal and then to the grid of the 6A8 and measured the signal amplitude on my scope at the speaker voice coil. I kept the signal level low so as not to saturate the AGC. The P-P voltage level, and also the audible 400Hz tone, was 2-3 times higher when the generator was connected to the antenna terminal! I also have the chassis connected directly to house ground and the RF gen. coupled through a 0.01uf cap.
However when I touch first the antenna terminal and then the grid of the 6A8, making my body an antenna, the signal level is much higher when I touch the grid of the 6A8. This is the opposite of what using the RF gen. shows. Don't know why the difference.
Steve D
Moisture absorption comes to mind. It would be worth a try to remove the coil and carefully bake it in the oven for 30 minutes at no higher than 200 degrees F.
Make careful notes on how the coil connects in the circuit if you do this!
I cannot guarantee that this will work, but it is worth trying. If it does not help, replacement of the coil will probably be necessary even though it may show the proper resistances.