Hello Philco Restorers
This is my first post on this forum. I have a 38-12 that someone else started a recap. When I bought this totally dead radio at an antique store however, none of the resistors were replaced and the variable capacitor's isolating grommets were dry and crumbling and were not replaced. These are the repairs I have made so far. I also have installed a P-C70 Osc universal oscillator as a temporary fix and the radio has been working at the higher broadcast frequencies. I would like to use the stock coil in this radio rather than try to spend more time troubleshooting why the lower end of the BC band is not being received with the universal oscillator coil.
Unfortunately every one of the four wires on the original oscillator coil are hanging and loose from whichever solder lug they once were connected to. So I am wondering if anyone that has rewound the original 38-12 oscillator coil has a sketch of which solder lug the top and bottom of both the primary and secondary coil windings were connected to? My second question is what was the original wire size was for both the primary and secondary coil windings? On my coil form, the wire appears to be two different sizes. Lastly, did anyone record the number of turns on each coil? Any help on rewinding this original Philco coil will be appreciated.
Ernie
Hi Ernie and welcome to the Phorum. Looking at the 38-12 schematic, it shows a diagram of the oscillator coil. There's an index notch on one end of the form that you can face toward you and down. The terminals will be at the top. Terminal one is above the index, terminal two is to the left, terminal three is on the right and terminal four is behind one. One connects to a 110pf cap, two is grounded, three connects to 6A7 grid 2 and four connects to B+. You may not need to rewind the transformer if you measure continuity between one to two (2.5 ohms), and three to four (3.5 ohms). Others will chime in with info on wire sizes. I'm thinking you may have to bake the form at 200 degrees a couple hours before rewinding.
Hi Rod and thank you for your helpful response. The information that you provided is helpful in that you reminded me about the index mark and the sequence of pin numbers which I had forgotten about. It was also useful to me when I wire the rewound coil back into the RF section. Unfortunately, when I started working on this radio I found only 1 of the four terminals on this oscillator coil still connected to a solder lug. That 1 wire is connected to pin 2 and was the end of the larger coil up at the end of the index mark. Every other pin had loose wires at the solder terminals end with no continuity to any other pin. These loose wires were hanging off the coil and and separated from the coil wire they were originally connected to. Since the wire connected to pin 2 was one end of the largest winding on the coil I can now infer how to wind this larger primary coil. Now I really need someone to give me information on how to wind the secondary. To be more clear I will need to know is the secondary coil wire connected to pin 4 also wired so that it terminates at the index mark end of the coil as is the case for pin 2 and does the winding connected to pin 3 terminate at the solder lug end or is it connected the other way from pin 2?
When I unwound the existing coil wire I found three breaks in the primary winding and about 5 breaks in the secondary winding. By eyeballing the unwound primary wire it appears close to if not identical to 32 gauge wire that I have. lf someone on the forum has rewound this coil and had success I'd love to know if my wire gauge guess is correct and if they used the same gauge wire for the secondary coil. The number of turns they used for each coil would be very helpful too.
Thanks once again,
Ernie
Hi Ernie,
Since you are already into rewinding the coils, another very important factor is the direction of the windings. They must be wound the same as the original or the oscillator won't oscillate.
It will anti-oscillate. The sinewave, when looked at with a scope, will move against the sweep.
Mike, now that's creepy. We spend a lot of time trying to get them to oscillate and then not oscillate. This confuses me.
What can I say.....radios are oscillatingly confusing folk.
I am appreciating the helpful responses I have been given so far...on the other hand, I am still looking for information on the second part of my query. Since 3 of the 4 pins except the wire from the primary coil on pin 2 had broken wires at the solder terminals end with no continuity to any other pin, I am uncertain about how to rewind and connect the secondary coil. Since the wire connected to pin 2 was one end of the largest winding on the coil I can now infer how to wind this larger primary coil. As I posted, I am trying to learn if the secondary coil wire connected to pin 4 is also wired so that it terminates at the index mark end of the coil as is the case for pin 2 and does the winding connected to pin 3 terminate at the solder lug end or is it connected the other way from pin 2?
Thanks,
Ernie
[
attachment=27377]Hello Ernie, here is a picture/diagram I drew of the oscillator coil in my 38-12. I carefully unwound the secondary and got 1 continuous piece of wire with no breaks. It measured 1.5 ohms; this is why I believe the schematic is incorrect as it says 3.5 ohms. Maybe when the schematic was printed, someone put the wrong number in. Just a suggestion. The original wire measured 1.5 ohms so I rewound using 34 guage wire and it measures 1.6 ohms; almost like the original. Hope this picture helps.