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philco model pt-4 - tonto007 - 05-08-2020

Hello,
Is part number 36-1533 required on this radio? If not, do I need to put a jumper in it's place?

RE: philco model pt-4 - Radioroslyn - 05-09-2020

Hi and welcome,
Can't  leave the circuit open. If you your use a jumper in it's place you'll have a lot of hum. Replace it with a 500 ohm 2w resistor and increase the value 30-2382 to 47mfd@160vdc. This will satisfy the electrical needs but may not provide any magnetism which the speaker requires.

RE: philco model pt-4 - tonto007 - 05-09-2020

Thank you for responding. What exactly is part 36-1533?

RE: philco model pt-4 - Nathan Slingerland - 05-09-2020

Look at the service info for the PT-4:

https://philcoradio.com/library/download/service%20info/yearbooks/1941/split/Part17-Philco%201941%20RMS%20Year%20Book.pdf

36-1533 is the field coil of the electrodynamic speaker (this is before the days where they could cost effectively make strong permanent magnets). The field coil doubled as part of the original filtering design.

RE: philco model pt-4 - Radioroslyn - 05-09-2020

A couple of thoughts. If your field coil is open you can do as I mentioned. The pole inside the spkr as some residual magnetism and it may work. How well it will work I'm not sure. I have heard of sticking a small rare earth (powerful) behind the fc at the back of the spkr to increase the magnetism.
The other option is the replace the spkr with a permanent magnet one. I think that this set uses a 4"x6" oval. These are not all at common. And the other trick is to be able to mount the output transformer on it's back. I'm not saying it's impossible but will take a little hunting to find a proper candidate.
GL

RE: philco model pt-4 - tonto007 - 05-09-2020

Terry,
Is 36-1533 an existing part of the speaker? If so, where is it located?

RE: philco model pt-4 - Radioroslyn - 05-09-2020

Yes. If you were to grab and rip it from the chassis you would have 4 wires hanging. 2 of them go to the transformer that is mounted on the top of the spkr. the other 2 are corrected to the field coil pn 36-1533. Don't rip the spkr out!

RE: philco model pt-4 - tonto007 - 05-09-2020

Terry,
Thank you for your input. Once I got my head out of my butt I found then leads & their connections....thanks again.
Gene

RE: philco model pt-4 - Radioroslyn - 05-09-2020

Here's an explode view of a generic eletrodynamic speaker.
https://www.quora.com/Can-I-use-an-electromagnet-instead-of-a-permanent-magnet-in-speakers

RE: philco model pt-4 - Radioroslyn - 05-09-2020

If you measure the resistance from pin 4 of the 50L6 to pin 7 of the 35Z3 you should see 500 ohms or so. If it's way higher your fc is suspect. Just for grins measure the resistance from pin 3 of the 50L6 to pin 4 of the 50L6. Should see several hundred ohms.