The PHILCO Phorum
Bad coil - Printable Version

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Bad coil - Forrest - 12-05-2019

Hello I am a new member with a problem, maybe some one else has run into this. I have a 37-84 code 121 the oscillator transformer secondary winding going to the cathode of the detector oscillator tube was open I was able to find out it was 3 windings up from the bottom of the coil so I reconnected the winding leveing out the 3 windings it plays but poorly compensator has to be at minimum capatance to get only low band, will 3 windings make that much difference? Dose any one
Rewind theses coils?
Forrest

RE: Bad coil - klondike98 - 12-05-2019

Welcome to the Phorum!
Icon_wave

RE: Bad coil - morzh - 12-06-2019

You need to rewind.
If it opened in the winding it likely oxidized.
The coul is compromised.
Plus you might want to get rid of the old celluloud insulation under the winding.
Rewind only the coils that show oxidation.

RE: Bad coil - Forrest - 12-06-2019

Thank you for the reply.
I was afraid of that looks like it will be a pain to do.
Forrest

RE: Bad coil - Simon Wa3uay - 12-06-2019

that is sage advice! I have a 19B with same problem! plus the primary is bad also. So, let us know how it goes, Forrest, I will be doing the same thing.
Simon

RE: Bad coil - Forrest - 12-06-2019

Ok shall do, need to order 34 ga wire.
Forrest.

RE: Bad coil - Radioroslyn - 12-06-2019

Hi Forest and welcome,
It's not an unusual issue for the 1928-35 Philco sets to have open primaries on their ant, rf, and oscillator coils. By 1936 Philco changed the design of the coil so that the windings are not over top of each other and no celluloid strip. But there are a few exceptions and guess what the 84/37-84 is one. The good news is that the winding it self is pretty easy to rewind. It's on the outside and doesn't require a lot of surgery to get at it.

One important point is to note the direction that the winding is wound. The new coil must be wound in the same direction (the phasing is important). If it is wound in the reverse direction the oscillator will not oscillate.

Just did one a month of so ago. A 2nd gen 84 (1935 model). My best recollection is that was 17 turns for the feedback or tickler winding.

Something else to check is the primary of the antenna coil. This can de accomplished by unplugging the set, turning the volume full up, the then measuring the resistance from the ant to the gnd posts. If all is well you should see a very low resistance like <10 ohms. If more some investigation is in order.

With either of these coils open the set will not work worth a tinkers darn. A bad osc coil will give you very poor sensitivity, stations won't track on the dial and tuning will be very broad. Bad antenna coil will give you poor sensitivity .

One last thing must use a signal generator to align the IF stage. Without it's difficult to get good performance from this little set.

GL.

RE: Bad coil - Forrest - 12-06-2019

Hi GL,
Thanks for the come back. You are rite I have very broad tuning, I didn't think a couple of turns would make that much difference. I think I counted 14 turns but I could very well be wrong will try 17 can always take some off. I was thinking of cleaning the old stuf of the coil then put a thin layer 
Of wax on and trying to wind by hand or fix to a variable speed drill at real low speed how did you do it?
Forrest.

RE: Bad coil - klondike98 - 12-06-2019

Here's some rewinding info from Chuck Schwark's site that might be helpful. Not your model but still ...

RE: Bad coil - Radioroslyn - 12-06-2019

Hi Forest,
>I didn't think a couple of turns would make that much difference

As Nippsey Russell use to say "Oh Yeah!". With the feedback coil open two things happen. Since the cathode isn't grounded anymore the 77 mixer tube isn't going to do much of any thing. The other thing is that with out any feedback the oscillator isn't going to run. This means that there is no frequency conversion ( from the frequency of the dial to 460kc ). The other 77 is looking for a signal @ 460kc and it's getting a weak signal @ the frequency that the dial sez. This is why the tuning is broad. Oh I think the Kingfish said it a few times too when scamming Andy into a scheme.

>I think I counted 14 turns

I'd trust your counting over my memory!

>trying to wind by hand or fix to a variable speed drill at real low speed

By hand. I do reserve some winding to the drill but this is pretty quick and easy. Have used the drill for rewinding a few Philco shadow meters which is abt 1200' of #40 Ga wire.

For those following at home the 37-84 code 121 is the same as the older 84 1934-36.The late alliteration of the 84 was the 37-84 code 122 which is the same set with octal tubes. Pretty sure both used the same photofinish cabinet along w/a few others.
Obtw GL is the abbreviation for good luck. Name is Terry it happens all the time not a problem.

RE: Bad coil - Forrest - 12-08-2019

Thanks much for the come back information always helps I have the wire ordered.
Forrest. Icon_wave

Bad coil update. - Forrest - 12-22-2019

Thanks to all who helped me with advice on rewinding my oscillator coil.stupidity ruled for the first two attempts, luckily I had another almost identical radio pulled that coil and found out I was winding in wrong direction, now it works perfect.
Forrest

RE: Bad coil - Ron Ramirez - 12-22-2019

Congratulations.

I merged your last post into this thread because the post by itself in its own thread lacked context. Putting it here puts it into context. Icon_smile