[MarkinK-zoo]

Hi, all.  The primary on the RF coil is open.  You will note on the 37-620 code 125, the BC transformer has only a secondary winding.  The primary on the police/sw band coil apparently supplies the BC as well.  So I am stuck about how to replace or repair this.  I can find a replacement RF coil on AES, but that coil obviously has the primary and secondary together, not like it is on my Philco. Any ideas?   Thanks.   Mark

[klondike98]

Welcome to the Phorum!


For those following along in this thread here's the link to the schematic: LINK
UPDATE: this link is for Code 121, the correct schematic is found below in Post #6

[Chas]

I am referencing the schematic provided...

IMHO only a replacement (Philco) RF transformer for the BC band will be a drop in fit.

Alternately it can be rewound.

Although the schematic is just a line drawing of the RF coil, it appears to have a combination of solenoid and universal winds.

Stated, the primary is open, that could be the universal wind.

It is possible to scramble wind that primary as it is not tuned.

Scramble wind  is a compromise, best advise is not to compromise on any other coil parameter such as the turns and wire size & type.

A Morris winder could reasonably replicate the universal wind...

GL

Chas

[MarkinK-zoo]

Ah, thanks for replying Chas, but can you translate that for me!   I don't have any equipment for winding coils.  Can you direct me to someone who can?   Thanks.   Mark

[MarkinK-zoo]

Bob, the link to the schematic you included is not the code 125, so it is not the same as my radio. The earlier version 37-620 has a different RF transformer with primary and secondary coils. The code 125 has only a secondary coil.

[MarkinK-zoo]

         I am attaching a scan of my schematic since it is hard to find.

[Nathan Slingerland]

Hi MarkinK-Zoo,

Andy Sorrell and I have been building up the library of scanned service bulletins in the Philco Library.

Have a look here and enter `37-620` in the search box:
https://philcoradio.com/library/index.ph...bulletins/

Service bulletin 251A is for the 37-620 (Code 125).

[Chas]

Ah, thanks for replying Chas, but can you translate that for me!   I don't have any equipment for winding coils.  Can you direct me to someone who can?   Thanks.   Mark

I do not know of someone who would wind or repair an RF coil as a hobby for others.

Post SHARP well lighted images of the defective coil. It will have to be removed from the radio.

Use colored pens or paints to mark the connecting wires. If you can find any other data on the chassis, occasionally, the coil will have a red or other bright color reference mark, record that to your notes...

When removing the coil for its photo session use great care not to disturb the wiring as little as possible.

Post the coil images, indicate your chassis variation, a WTB in the Phorum classifieds.

I'm sure that some collectors have coil "junk" boxes but may not know where the coil came from. So, comparison images will help.

A single, even a double layer solenoid wind for the BC band can be replicated by hand with no tooling..  Opps, will need a micrometer to measure the wire.

New supplies:

Wire, bees wax,   >>>>  patience...  <<<< 

GL

Chas

[MarkinK-zoo]

Chas: the schematic I posted is correct. The link to a schematic that Klondike98/Bob included is not correct. So, you hopefully you are able to see what you need on the image in my post. I would be willing to rewind the coil by hand, but measuring the gauge of the wire sounds like a challenge to me. I can buy a micrometer, but it all looks as fine as human hair to me and I can't imagine being able to tell the difference. Mark

[MarkinK-zoo]

Nathan: Thanks for the link, but I have all of those pages. Years ago I ordered it from AES because I couldn't find a free download at the time. Mark

[MarkinK-zoo]

I have read about by-passing defective IF stages using a capacitor to connect the plate of one tube to the grid of the next and by-passing the open winding with a resistor. Would this work for an RF stage? There would be some loss of performance I would assume, but it would be way better than what I have now. Can this done? Mark

[MarkinK-zoo]

Well, I think I answered my own question. I followed an article I had down loaded years ago about by-passing defective IF transformers and tried this with my defective RF transformer. The performance was worse. So I guess either finding a replacement (unlikely) or rewinding (not really wanting to do this!) are my only options.

[Nathan Slingerland]

MarkinK-zoo - I think I may have a 37-620 parts chassis. Will check tonight.

[MarkinK-zoo]

Well, Nathan, wouldn't that be fantastic!

[Nathan Slingerland]

Sorry to say I checked and I don't have a 37-620 chassis.