Philco 39-7 Alignment Problem - Printable Version

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+--- Thread: Philco 39-7 Alignment Problem (/showthread.php?tid=19761)

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Philco 39-7 Alignment Problem - Stonewall - 03-16-2019

I've completed a rebuild of a Philco 39-7, but there is an issue with the alignment instructions from Philco that I cannot resolve.  Does anyone know how to adjust the "6A" trimmer capacitor that is in parallel with the oscillator coil?  Nowhere do the official instructions from Philco mentioni how to do that.  I've finding the tuning alignment across the dial to be very difficult.  My experimentation leads me to believe that the "6A" trimmer holds the key.  Any ideas?

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RE: Philco 39-7 Alignment Problem - Ron Ramirez - 03-16-2019

6A is a 20 pF fixed capacitor used only in model 39-7; 3B is the oscillator trimmer.

The alignment instructions state that both 3B and 3A should be adjusted at 1550 kc.

https://philcoradio.com/library/download/service%20info/yearbooks/1939/split/Part17-Philco%201939%20RMS%20Year%20Book.pdf

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RE: Philco 39-7 Alignment Problem - Stonewall - 03-16-2019

Very interesting.  On the radio I've rebuilt, "6A" is definitely a trimmer cap from pin 1 of the oscillator coil to ground.  I suspect that someone modified the radio at some point, but there's no indication of any other modifications at all.

Thanks much; that certainly points me in a different, maybe more productive, direction.

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RE: Philco 39-7 Alignment Problem - Ron Ramirez - 03-16-2019

The Philco service sheet clearly indicates 3B as the oscillator trimmer. That's all I can say about it.

It's been a while since I owned a 39-7. 6A could be one of those "semi-fixed" trimmers Philco used in some models of around that period (1938-39), which looks like a trimmer cap but was adjusted and sealed at the factory. Why they did this rather than using a fixed mica cap, who knows other than some models needed more or less capacitance?

If this is the case, do not make any attempt to adjust 6A.

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