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Philco 39-7C Restore - Printable Version

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Philco 39-7C Restore - klondike98 - 04-15-2024

I started working on the 39-7C I got recently. The link to the schematic is https://philcoradio.com/library/download/service%20info/yearbooks/1939/split/Part17-Philco%201939%20RMS%20Year%20Book.pdf

Overall it looks relatively decent. There is rust on the back of the chassis but most of the chassis is rust free. It has the usual crumbling rubber insulation for this vintage and all the tubes test good except the 6A7. All of the transformers ohm out OK except for the secondary on the antenna transformer. The 5 ohm section between lead 3 & 4 is open. I'm not quite sure what I'm going to do about that.

[Image: https://www.dropbox.com/scl/fi/6i0ljg88dznwyea9xcos4/Philco39-7C_03.jpg?rlkey=u6l4eiazvip2206qmwih6kieq&raw=1]
[Image: https://www.dropbox.com/scl/fi/06u793mwule23rzn1mrlq/Philco39-7C_04.jpg?rlkey=qhid7f9ac1sn6tc9n9fbtstjl&raw=1]

RE: Philco 39-7C Restore - Paul Philco322 - 04-15-2024

Looks as if no one has been hacking around in there, so that is a help, good luck.

Paul

RE: Philco 39-7C Restore - morzh - 04-15-2024

Bob, yeah. The secondary is critical, as it is part of the tuning.
Is it a simple bobbin, easy to rewind, or one of those "cross-wound" wax-dipped jobs?

RE: Philco 39-7C Restore - klondike98 - 04-16-2024

I’m not sure Mike. I think I’m going to have to take apart to see. It looks like some kind of sleeve over the windings.

RE: Philco 39-7C Restore - morzh - 04-16-2024

Might turn out to be not too bad at all. Looks like a ragular one-layer coil. The sleeve..I guess you'll find out when it's off. Could be of some simple mechanical purpose.

RE: Philco 39-7C Restore - klondike98 - 04-16-2024

When I get back to it I’ll let you know, thanks.

RE: Philco 39-7C Restore - klondike98 - 04-17-2024

This is a Pittsburg PA area radio which is consistent with where it was shipped from. The automatic tuning buttons are set for KQV, WJAS, WCAE, KDKA, and WHJB which according to a 1940 Station Log in our Library are 1380, 1290, 1220, 980 and 620 on the dial. All are Pittsburg stations except WHJB which is Greeensburg (WHJB is currently 107.1 FM in Greensburg).

RE: Philco 39-7C Restore - klondike98 - 03-21-2025

I finally got back to working on this radio after almost a year. I even forgot that I had already started this thread and that the antenna transformer has a problem. As I mentioned earlier the wire insulation is crumbling for almost every wire in the set. The power transformer got my attention first and indeed there has been some heat I think.

[Image: https://www.dropbox.com/scl/fi/zbomdctv6irjfrjdj3vu8/Philco39-7C_05.jpg?rlkey=uzpmo75v6who8533j70m9x2b4&raw=1]

RE: Philco 39-7C Restore - morzh - 03-21-2025

39-7 should have the same or very close transformer as 38-12, and the junk chassis are many and available, in case you need one.

RE: Philco 39-7C Restore - klondike98 - 03-21-2025

Thanks Mike. It actually seems to be ok, at least it ohms out ok with no shorts. I will try getting the wires reinsulated.

RE: Philco 39-7C Restore - morzh - 03-21-2025

Bob

Transformer may heat up for reasons that are not its own; it could be loaded heavier than appropriate.
But if it did not sustain damage, it could be OK.
To me a good way of testing it is plugging it in 120V and running it with no load. If it does not heat up (could get a tad warm) considerably, it is OK (no turn short).
Ohming out is the first check, of course, but it will not reveal a turn short.
This test will.
(BTW this is one instance where I approve using a dim bulb tester).

RE: Philco 39-7C Restore - klondike98 - 03-21-2025

Thanks Mike, I will do that check. Just a bit of progress today but ready to put the shell back on and reinstall the power transformer now. I simply took off the old insulation by squeezing it a little with needle nose pliers. It just crumbled away. Then a colored heat shrink sleeve went over the uninsulated wire. I spliced in a longer piece of wire that will then get soldered onto the appropriate spot on the chassis. A quick ohm check after all the work and it still seems to be OK.

[Image: https://www.dropbox.com/scl/fi/oauwtcj0g5ixkj174t0vn/Philco39-7C_06.jpg?rlkey=du12sgvf8064fcrgne7eg5bug&raw=1]

RE: Philco 39-7C Restore - radiorich - 03-21-2025

Hello Bob,
Nice work on that trasformer !

Sincerely Richard