The PHILCO Phorum
91-221 coils - Printable Version

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91-221 coils - BWeismann - 01-19-2021

schematic:  http://www.nostalgiaair.org/pagesbymodel/884/M0013884.pdf



I'm hoping to get some guidance on coils, specifically, the antenna/RF coil, #2.

I've yet to rewind one, but have watched a lot of Youtube about it.

Mine has an open inner primary (the antenna side).

Schematic shows it should have resistance of 24 ohms.



It's not an outer, smaller winding over a larger winding, like I've seen in various posts/videos.

It's like a bobbin inside the tube at the opposite end from the terminals.




If anyone can tell me what my next step is, I's sure appreciate it.

Thanks.

RE: 91-221 coils - Radioroslyn - 01-20-2021

Unsolder connections on bobbin and remove. You can try to find the break if you like and repair. Or measure out 24' of 40G copper wire and rewind it on to the bobbin direction is not important.

RE: 91-221 coils - BWeismann - 01-20-2021

Thanks, Terry.
I've got a few more questions.
1. Should it be bare copper wire or enameled, etc.
2.  Do you know of a good source for said wire?
3.  Any tips as to removing that bobbin without damaging/distorting the main tube and its coils?

As you likely know, it's riveted to a piece of material that is then fixated in 2 slots at the end of the tube.  Initial inclination is to distort the tube and then pull the tabs out with a needle nose.  Will I be jeopardizng the other coils (from 1932) with such a move?  What's a safe way to get it done?

RE: 91-221 coils - Radioroslyn - 01-20-2021

Hi,

1. Should it be bare copper wire

No as it would just electrically look like a short.
or enameled, etc. Yes.

2.  Do you know of a good source for said wire?

I don't really have any favorites as I've been doing this for a long time. Would pickup a few rolls here and there at radio swaps and hamfests. If you needed a larger gauge wire sometime a motor rebuild shop is a good source. They have end of spools that are enough to fix up a coil or two and some times they can be talked out of them. About the smallest they carry is 24 or 26G.
Normal channels like Amazon or Ebay should ok to find the 40G

3.  Any tips as to removing that bobbin without damaging/distorting the main tube and its coils?

I did one a yr or so ago but I don't really remember the blow by blow description. I would do this. If the tabs sticks past the edge of the coil form sand them down with a Dremel so they are even with the form's sides. Use a heat gun to warm the top of the form up a bit (not trying to set it on fire or melt it or any like that). See which part has more give the coil form (I would think) or the tabs holding the small coil in the center. If it's the form squeeze it a little to release the tab. If it's the tab stick a dowel thru the center of the form and push it out.
Or you could take your dikes cut the top of the form on one side to release the tab. With one side gone it should come out easily. Use a dab of hot glue to reinstall it.

  Will I be jeopardizing the other coils (from 1932) with such a move?  What's a safe way to get it done?

The easiest the safest would would be to cut one side of the top of the form where the tab is held in.

RE: 91-221 coils - BWeismann - 01-20-2021

Thank you, Terry.
That gives me a path to pursue. I've already re-stuffed all the bakelite block caps.
I'll likely be back on the Phorum for this one, as the detector coil has a short and the oscillator coil also has an open winding.

I'm learning a lot on this one, from re-stuffing Mershon capacitors, rebuilding bakelite blocks, and now, chasing down coil issues.

It's a 25 Hz, double speaker, console I got down the street for $10. 
I'll get some life out of it yet!

RE: 91-221 coils - Phlogiston - 01-20-2021

https://temcoindustrial.com/shop/wire-cable-accessories/magnet-wire?amount_of_wire=176%2C175&wire_gauge_awg=162

RE: 91-221 coils - BWeismann - 01-20-2021

Say, do you need to try to 'strip' enamelled wire before soldering or does the heat just take care of it?

RE: 91-221 coils - Phlogiston - 01-20-2021

On most new wire (single coat) heat will do it.

RE: 91-221 coils - Radioroslyn - 01-20-2021

Or something like this: https://www.ebay.com/itm/40-AWG-Gauge-Enameled-Copper-Magnet-Wire-2-oz-4152-Length-0-0034-155C-Natural/322231509251?epid=1380697764&hash=item4b067ea103:g:iZYAAOSwgQ9Vw7C2

RE: 91-221 coils - BWeismann - 01-21-2021

I cut the end of the tube in 2 places on one side down to the tab and it lifted right out.
Unwound it, found an obvious break, but the 'insulation' was poor along entire length.
For what it's worth, 36.5 feet of wire was wrapped on the small wooden spindle in a counterclockwise fashion.
The coil was labelled with the number 38 on the tape that secured the outer part of the winding.
Not sure how you could ever repair it besides rewinding it.
Gotta order my wire.