Philco 89B, Detector coil repair - Printable Version
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+--- Thread: Philco 89B, Detector coil repair (/showthread.php?tid=20073)
Philco 89B, Detector coil repair - rck46 - 06-05-2019
I posted several days ago on the WANTED forum looking for a replacement coil. See https://philcoradio.com/phorum/showthread.php?tid=20069. After reading the posts there and discussing with Terry via PM I may consider trying to rewind the open coil.
The open coil is the small primary winding. I have posted several pictures of the coils condition. In PM discussions with Terry it looks like I could rewind with 25 turns of 34 gauge wire and the direction of the winding is not of concern.
My problem is the removal of the old winding and what looks like the melted remnants of the nitrocellulose material separating the two coils. Also wondering if the secondary coil may be damaged by the melted remnants although it does show continuity.
An comments or quidance is appreciated.
Thanks, Bob
RE: Philco 89B, Detector coil repair - rfeenstra - 06-05-2019
I've rewound several of these and have never had a problem with the wire underneath the primary. Once cleaned up, I usually coat the underlying wire with shellac before installing a replacement for the nitrocellulose.
RE: Philco 89B, Detector coil repair - rck46 - 06-05-2019
Is there a proceedure for removing the crusty remnants of the nitrocellulose?
RE: Philco 89B, Detector coil repair - Steve Davis - 06-05-2019
After unwinding the outer coil, most of the residue can be removed with your fingernail.
Steve
RE: Philco 89B, Detector coil repair - Radioroslyn - 06-05-2019
https://www.philcorepairbench.com/rewinding-philco-rf-coils/
Ignore the model numbers and # of turns as those are for early sets than yours but the procedure is the same. I've never done the ammonia thing.
RE: Philco 89B, Detector coil repair - Steve Davis - 06-05-2019
NO! do not use ammonia. Ammonia will corrode copper.
Steve
RE: Philco 89B, Detector coil repair - rck46 - 06-05-2019
I was able to remove what remained of the coil wire and nitrocellulose. Still have continuity on the secondary so guess I am good there. I will follow the procedures outlined in the above reference but avoid the ammonia. Any recommendation on cleaning other than ammonia? I counted the turns at either 13 or 14 - hard to tell because the wire was in a lot of pieces. Does that sound about right for the number of turns?
Bob
RE: Philco 89B, Detector coil repair - Radioroslyn - 06-05-2019
> Any recommendation on cleaning other than ammonia?
I would leave it alone. Any sort of cleaning may disturb the enamel coating on the secondary.
>Does that sound about right for the number of turns?
Sound good.
RE: Philco 89B, Detector coil repair - Steve Davis - 06-05-2019
The primary isn’t a tuned circuit so the exact number of turns is not super critical. I would go with the 14. If it doesn’t work well,it would be easier to remove a turn than add one.
Steve
RE: Philco 89B, Detector coil repair - rck46 - 06-06-2019
I finished it up today. Went with 14 Turns. Will be a while before I will be able to test it. Thanks for the help.
Bob