The PHILCO Phorum
42-321 Questions - Printable Version

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42-321 Checking field coil, audio trans & speaker - Paperboy - 10-26-2016

What is the procedure for checking continuity on the audio section of this radio?? I think my field coil is ok, hard to say about the rest. I do not have an audio generator yet. Thanks. That's a philco 42-321 that is.

RE: 42-321 Checking field coil, audio trans & speaker - Radioroslyn - 10-26-2016

Measure the resistance from the cathode of the 35Z3 to the plate of the 50L6. Should see 2k or less.

RE: 42-321 Checking field coil, audio trans & speaker - morzh - 10-26-2016

The field coil is measured between the two Plusses of #31 cap, can't see the value, looks like 530 Ohm, but should be under 1kOhm.

Terry gave you the measurement for the output xfmr primary.
The secondary is always fine.

Now the speaker itself is another matter: you cannot measure it unless unsolder one of the two speaker leads,
then measure between them to see the resistance of maybe 4 or 8 Ohms. Otherwise it is masked by the secondary low resistance.

RE: 42-321 Checking field coil, audio trans & speaker - Radioroslyn - 10-26-2016

Well if you measure from cathode to plate as I described it's telling you the series resistance of both fc and primary of the opt together, or did I miss something?

RE: 42-321 Checking field coil, audio trans & speaker - morzh - 10-26-2016

You're absolutely right Terry, I just missed the fact you were referring to both tubes. Yes, one stone with two birds. (I wonder what two birds can do to one stone......)

42-321 philco paper behind dial - Paperboy - 10-27-2016

There is a rectangular piece of paper behind the dial that is now Roached. Do I just use hard stock paper for this or is there another product I should use. Thanks.

RE: 42-321 Questions - klondike98 - 10-27-2016

Hardstock paper should do fine.  ( I merged your question with your other 42-321 thread and modified the title to keep the topic together ...  see the Phorum Rules.)  Icon_thumbup

RE: 42-321 Questions - Paperboy - 10-27-2016

Do you recommend removing #8 capacitor and choke assembly, I understand this is a trap for old ship to shore frequencies and possibly trap for stray reactances from old capacitors which will be changed to new ones. Just wondering if I could get rid of it or just keep the coil and replace the cap.
Thanks for all the replies fellas.

RE: 42-321 Questions - morzh - 10-27-2016

Unless it is all broken up and threatens the whole radio integrity, there is no harm in leaving it alone. If a cap is a paper one and is leaky....could be removed. I think either way it does not affect the operation much.

RE: 42-321 Questions - Radioroslyn - 10-27-2016

What I've done is pull the innards out of the cap and restuff it with a new one leave the coil in place. Electrically the cap provides a ground from B- to the chassis so I would leave the cap and connect it from B- to the chassis without the coil.

RE: 42-321 Questions - morzh - 10-27-2016

Well, I assumed (without looking in the sch) we were talking about the trap that usually goes in the antenna circuit; in this case what I said is not correct, and I agree with Terry: you do not necessarily need the coil but you do need the cap. Without this cap you might have a whole lot of howling and motorboating.

RE: 42-321 Questions - Paperboy - 10-28-2016

I tested the field coil several ways and got a open circuit every time.
What do you suggest, PM speaker with multi watt resistor in place of choke??
Haven't peeled the paper back yet to see if prob is on outside.

RE: 42-321 Questions - Radioroslyn - 10-28-2016

http://www.nostalgiaair.org/pagesbymodel/512/M0013512.pdf

Value of the resistor isn't particularly critical as it's in the positive side of the hv. If it was in the negative side then it would change the amount of negative bias voltage available. So looks like the original is about 500ohms, I would go a bit higher around 1000-1500ohm @ 2-5W. You'll need to boost the value of the filter caps too as the resistor isn't very efficient at eliminating hum like a choke is. Would use 2-47mf @160v.

RE: 42-321 Questions - Paperboy - 10-28-2016

I ohm'd out the RF transformer (part #11).
The secondary gave 30 ohms but the primary
showed infinity. Is it easy to find this part or do I have to find another 42-321.
Thanks

RE: 42-321 Questions - Radioroslyn - 10-28-2016

(10-28-2016, 11:02 PM)Paperboy Wrote:  I ohm'd out the RF transformer (part #11).
The secondary gave 30 ohms but the primary
showed infinity. Is it easy to find this part or do I have to find another 42-321.
Thanks

I would wind 50 or 60 turns of sm magnet on the coil form like 36ga wire. It's untuned so it not super critical. Or you could use a rf choke in place of that winding and use a small mica cap like 50pf from the plate of the rf amp to the input grid of the mixer tube. Or this https://www.tubesandmore.com/products/antenna-coil-tube-radios