09-11-2008, 11:14 AM
I decided I could not live with my originally proposed fix, so I decided to try and repair the coil. In the photo below, the Short Wave oscillator coil is the one to the top left. You will notice it is the only one with a DOUBLE form.
[Image: http://mcclellans.com/3761.jpg]
I first removed the coil from the RF Subchassis assembly - not an easy task! I noticed that the top lead of the OUTER coil, which is about #20 wire, passed all the way through the coil (both the inside and outside forms). So I pulled it back through the coil and then secured it with tape to prevent the outer winding from unwinding (held only by wax at this point). It was obvious by looking from the bottom that the inner coil form did not extend the whole length. Next I inserted a 25 watt pencil soldering iron tip into the top of the coil and moved it around to free the inner coil form. I correctly guessed that it was only held by wax. Once the wax on the OUTSIDE of the coil form started to melt, I was able to push out the INNER form using a screwdriver.
After the wax was melted off the inner coil form, the Philco green disease was obvious! I started unwinding the coil, but it was broken at about the same place on each turn. I removed the entire coil. The impressions left made it obvious how many turns were needed, as well as the winding direction. IIRC, I think it was about 16 turns. I rewound the coil using #38 cotton covered enamel wire. Once continuity was determined, the inner coil was re-inserted into the outer coil form (the trick is to align it so that the top of the outer coil can be reinserted through both forms).
The coil was then reinstalled and tested. We'll see how it works once I complete the restoration.
The RF subchassis restoration is complete - with all caps restuffed and one resistor replaced.
[Image: http://mcclellans.com/3761.jpg]
I first removed the coil from the RF Subchassis assembly - not an easy task! I noticed that the top lead of the OUTER coil, which is about #20 wire, passed all the way through the coil (both the inside and outside forms). So I pulled it back through the coil and then secured it with tape to prevent the outer winding from unwinding (held only by wax at this point). It was obvious by looking from the bottom that the inner coil form did not extend the whole length. Next I inserted a 25 watt pencil soldering iron tip into the top of the coil and moved it around to free the inner coil form. I correctly guessed that it was only held by wax. Once the wax on the OUTSIDE of the coil form started to melt, I was able to push out the INNER form using a screwdriver.
After the wax was melted off the inner coil form, the Philco green disease was obvious! I started unwinding the coil, but it was broken at about the same place on each turn. I removed the entire coil. The impressions left made it obvious how many turns were needed, as well as the winding direction. IIRC, I think it was about 16 turns. I rewound the coil using #38 cotton covered enamel wire. Once continuity was determined, the inner coil was re-inserted into the outer coil form (the trick is to align it so that the top of the outer coil can be reinserted through both forms).
The coil was then reinstalled and tested. We'll see how it works once I complete the restoration.
The RF subchassis restoration is complete - with all caps restuffed and one resistor replaced.
