10-29-2024, 03:41 PM
Only thing between me completing this lengthy restoration of a 37-690 is getting the Magnetic Tuning to function. I have verified the variable caps and the coils inside the can are all OK, the associated wiring has been meticulously verified correct, all Philco block caps have been replaced, resistors checked or replaced, and I have the correct voltages on the Mag Tuning 6K7G. I have aligned the set per the instructions, but the Mag Tuning is not operating.
Clues:
1- While aligning at the IF of 470KC, the Primary (padder capacitor) of the Mag Tuning compensator (119P) has no effect (step 4). I have checked the trimmer itself, and the plates and mica separator appear fine. There is no resistance across it, my meter does not show any capacitance, but that may be a red herring since I am not sure if my multimeter is able to measure that low of capacitance. Also see #3 below.
2- The test where you turn the Mag Tuning on and off ("In & Out"), instead of no change in signal strength, with the Mag Tuning "on" the signal gets much weaker! (goes off freq).
3- At the risk of obfuscation, there is one more clue. While adjusting the Secondary (119S) per the Mag Tuning Adjustment section, I used 1000KC as my freq on the dial and Signal Generator. At this freq, if I adjust the primary 119P, the one that is supposed to be adjusted at 470KC, the signal does respond to adjustment. But alas, the Mag Tuning will still not work.
Does anyone who has aligned a set with Mag Tuning have any insight or additional tests to isolate the problem?
Clues:
1- While aligning at the IF of 470KC, the Primary (padder capacitor) of the Mag Tuning compensator (119P) has no effect (step 4). I have checked the trimmer itself, and the plates and mica separator appear fine. There is no resistance across it, my meter does not show any capacitance, but that may be a red herring since I am not sure if my multimeter is able to measure that low of capacitance. Also see #3 below.
2- The test where you turn the Mag Tuning on and off ("In & Out"), instead of no change in signal strength, with the Mag Tuning "on" the signal gets much weaker! (goes off freq).
3- At the risk of obfuscation, there is one more clue. While adjusting the Secondary (119S) per the Mag Tuning Adjustment section, I used 1000KC as my freq on the dial and Signal Generator. At this freq, if I adjust the primary 119P, the one that is supposed to be adjusted at 470KC, the signal does respond to adjustment. But alas, the Mag Tuning will still not work.
Does anyone who has aligned a set with Mag Tuning have any insight or additional tests to isolate the problem?
RJ Dial
"Radiodial"
Mendocino, CA
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