Philco 84 Open Field Coil - Printable Version

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+--- Thread: Philco 84 Open Field Coil (/showthread.php?tid=20127)

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Philco 84 Open Field Coil - PAradiogeek - 06-18-2019

I was given a rather nice Model 84 by a co-worker about a year ago.  In the process of checking it out, I found it has an open Field Coil.  After procrastinating for a while, I've decided to attempt to repair the break.  The image below shows the field coil mounted on the speaker.  I have a couple of questions before I start.

1) The arrow in the picture points to what appears to be a paper 'band' that wraps around the outside of the coil.  What was the purpose for this wrap?  Was this there to provide strain relief for the solder joint that joins the rather large wire, with the small field coil wire?

2) Assuming that the paper band was for strain relief, any thoughts on how to put another band around the connections when I'm done repairing the coil and/or the connections? Ideas on what to use to do this?

3) One of the two connections to the coil is at the top of the coil as seen in the image.  The other is buried beneath the big "U" bracket that holds the coil to the speaker frame, roughly 90 degrees clockwise from the one you can see.  The connection at the top looks to be rather easily accessible, and I'm hoping that the break is there.  If that turns out not to be the case, any ideas on how to get to the other connection?

4) Any general ideas on things to remember to do, or not to do, as I'm doing this?

   

Thanks,
Jon

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RE: Philco 84 Open Field Coil - Steve D - 06-19-2019

The wrap protects the coil windings and the terminations of the fine coil wire to the hookup leads. When I rewound my field coil I re-used the paper band and secured it with a few layers of friction tape.  Friction tape holds securely and looks original.

Typically field coils are not secured to the pole piece and are free to rotate. Once you disconnect the field coil hookup wires you should be able to rotate the coil to gain access to the start lead. If the break is at the finish wire connection you can unwind a few turns to get enough wire length to re-solder the connection.  My field coil from a RCA V-210 was 1100 ohms and had 10,000 turns of 34AWG wire so a few turns will not matter. 

If the break is at the start wire, hopefully there is enough wire lead left to re-solder it. It is almost impossible to remove turns from inside the coil. If the break is internal then the field coil will have to be re-wound which will require removing the cone/voice coil, pressing the pole piece out with an arbor press and rewinding it.  This will become quite a chore and perhaps it might be better to locate a replacement speaker or use a permanent magnet type with a 10H or so choke to replace the field coil for ripple filtering.

Here is a link to a thread showing my field coil re-winding:

https://philcoradio.com/phorum/showthread.php?tid=19722

Good luck,

Steve D

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RE: Philco 84 Open Field Coil - PAradiogeek - 06-19-2019

I appreciate the information Steve.  I'll be diving into it over the weekend.

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