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Philco 39-7 not tracking
Jimradio
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Posts: 194
Threads: 34
Joined: Jul 2016
City: Spring Lake MI
#1

09-25-2023, 02:20 PM
Restoring this 39-7, first I changed the electrolytes (2) then tested the radio. It played but I noticed the dial was way off and not tracking, the pointer is correct to the variable capacitor. I replaced all paper caps brought the radio up, the voltages looked okay, but still have a bad tracking problem. Example station 1370 comes in at 1200 the lower end is closer but still off. I did an alignment the IF went well. Tried to do the second step at 1550 KC adjusting 3B and 3A did nothing.
I believe 3B is the oscillator.
This is first for me the dial not tracking properly.
Help!
Jim
Spring Lake MI
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Chas
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Posts: 658
Threads: 8
Joined: Apr 2018
City: S. Dartmouth State, Province, Country: MA
#2

09-25-2023, 08:46 PM
Jim,

I do not "know" this radio...

The schematic gives me a clue and your description, something is not working correctly in the oscillator circuit .

Check the DC resistance of the oscillator coil, please use a VOM. It should closely agree to the published values. Lift one side of the 110pf mica cap #5 attempt to measure if you can looking for +-5 pf. Or, sub in a new 110pf dipped silver mica. Do not twist the old cap to measure. Cross check your cap measuring device with a new mica cap. Trust the new cap when comparing the old.

Any alignment adjustment that does not have an effect has a problem in its associated resonant circuitry, Bad coil(s) leaking condensers, dramatically changed resistors.

Any corrective work in the oscillator or RF, even pushing a wire out of the way, will affect alignment.

If there is a altered value of resistance in the oscillator coil AND there is a celluloid liner between the primary and the secondary, quite possibly there is corrosion to the coils...
 From A. H. Ghirardis Radio Troubleshooter manual, note, does not address calibration errors...

Sorry, it is a snip of a poor PDF. Download and open in an image processor to enlarge.

   


If the tuning condenser is mounted on grommets, if these sag will that effect calibration?

Chas
Pliny the younger
“nihil novum nihil varium nihil quod non semel spectasse sufficiat”
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Jimradio
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Posts: 194
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Joined: Jul 2016
City: Spring Lake MI
#3

09-26-2023, 01:23 PM
Thank you Chas
I found the problem it was capacitor # 6a 20 pf. when I replaced it all is well.
Love this forum.
Jim
Spring Lake MI
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Chas
Senior Member
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Posts: 658
Threads: 8
Joined: Apr 2018
City: S. Dartmouth State, Province, Country: MA
#4

09-26-2023, 03:24 PM
Icon_biggrin 

Happiness is not having to rewind the oscillator coil Icon_thumbup
Pliny the younger
“nihil novum nihil varium nihil quod non semel spectasse sufficiat”
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