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37-690 Bass Choke Replacement - Printable Version

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37-690 Bass Choke Replacement - Radiodial - 11-27-2024

While troubleshooting the no bass amplification issue, I think I found the culprit. The choke #104 is reading 164K ohms. My first thought is replace it with a 2K 5W resistor and increase the 1uf electrolytic, just like you would for a speaker, but that parallel 40K resistor threw me. How do I factor that in?

RE: 37-690 Bass Choke Replacement - morzh - 11-27-2024

https://philcoradio.com/library/download/parts/catalogs/1942/Philco%20Parts%20Catalog%201942.pdf


This is the parts catalog.

32-7528 choke is 65H, 10mA, 2,250 Ohm inductance.
Find a suitable one.

RE: 37-690 Bass Choke Replacement - Radiodial - 11-27-2024

Ah, now where to find one.
I've into this before on smaller sets, I now recall. Hammond makes one that is only rated 8MA, and this 37-690 has two stages of bass amplification, so 8ma may be pushing it.

RE: 37-690 Bass Choke Replacement - morzh - 11-27-2024

Yes, I just had to deal with that while repairing the 37-604 Philco. Exactly that value choke was gone. And the current was borderline.
So I used a smaller one with larger current, padding it with a resistor.
However, mine was the DC filter, whereas yours is an audio filter, so you need more precision.
Mine was 32-7569, which is same as yours (maybe different dims) - 65H, 10mA.

I used 154E, 2hich is 20H, 20mA.
There is also 30H 600 Ohm one, 157G. Two in series plus a 1k resistor. Those are small chokes too.

https://www.mouser.com/datasheet/2/177/153_159-736947.pdf
https://www.mouser.com/c/passive-components/inductors-chokes-coils/?inductance=20%20H&m=Hammond

RE: 37-690 Bass Choke Replacement - Radiodial - 11-27-2024

Yeah, I know, Mouser and Digikey don't have "big iron" components. For some reason Philco was messing with the 2250 ohms resistance of this common Philco choke by paralleling that 40K resistor. I wish I was smart enough to understand why. Seems to fine tuning it down to 2.1K?