Welcome Guest! Be sure you know and follow the Phorum Rules before posting. Thank you and Enjoy! (January 12) x

Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5

Magnetic Tuning Alignment
#1

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?


Attached Files Image(s)
               

RJ Dial
"Radiodial"
Mendocino, CA




Users browsing this thread: 1 Guest(s)
[-]
Recent Posts
Philco 42-345 Restoration/Repair
Ok MrFixr55,  I have tried the DeoxIT D5 on the band switch and even though it has relieved the tension I felt when turn...osanders0311 — 11:11 AM
Part numbers to model cross
Is there a reference somewhere where you can punch in Philco part numbers and see what models those parts were used in?Jim Dutridge — 10:17 AM
Philco 42-345 Restoration/Repair
Hi OSanders, Look carefully at the band switch. Turn it slowly and "wiggle" it around the desired band. ...MrFixr55 — 12:33 AM
5U4 vs 5Z4 tubes
I think that RCA and GE introduced metal tubes in the USA in 1936.  I don't know if they were being made by RCA, GE or b...MrFixr55 — 11:20 PM
Philco 42-345 Restoration/Repair
Vlad95, Thank you for the stringing guides and wow there are so manyosanders0311 — 06:01 PM
5U4 vs 5Z4 tubes
A pre war Hallicrafters, and an early one too, very nice! 1936 is pretty early for metal tubes too, which would explain ...Arran — 05:58 PM
Philco 42-345 Restoration/Repair
Thanks Rod, "When you hear the background hiss and no station it usually indicates that the oscillator quit" ...osanders0311 — 05:52 PM
Philco 42-345 Restoration/Repair
RodB :beerchug:Vlad95 — 10:22 AM
Philco 42-345 Restoration/Repair
Vlad, you nailed it. Swiss and German roots.RodB — 09:54 AM
5U4 vs 5Z4 tubes
Well this is a Hallicrafters SX/9 circa 1936. No real issues so far although I dodged a real bullet with a cap that was...bridkarl — 07:59 AM

[-]
Who's Online
There are currently 1488 online users. [Complete List]
» 1 Member(s) | 1487 Guest(s)
Avatar

>