[harley92]

I am restoring a Philco 37-620 with a burned field coil in the speaker. The number on the coil is 32-9008. looking through a Philco parts book, the coil is rated at 65ma and the schematic shows 1140 ohms.

I wish to replace the speaker with a pm speaker and use a choke to replace the field coil.

Can anyone tell me how many henries the replacement choke should be? Could I replace it with a resistor without changing the value of the electrolytic caps?

Any help would be great.

Thanks,
Gerald D.

[morzh]

If you replace it with a resistor (which will be a high wattage one) it should be a close match in ohms to the coil (1100 - 1200 ohm) to keep the DC voltages the same.
Keep the value of the first electrolytic cap (the one across the rectifier tube) the same.
You could safely double the value of the cap after the resistor to compensate for the lack of inductance in the filter. Or even triple.

[harley92]

Thanks for the help.
I have a tester to check the inductance of a like field coil, but it would only use 1khz as the test not the 120hz the coil would use. It came up with 70 Henry's which I didn't think was correct.
I'm sure the resistor method will be cheaper.
Thanks again.

[morzh]

A typical inductance of a choke in the filter is a few Henrys. 10H is not unheard of.
A resistor will probably work fine. In fact in many tube amps (like EICOs) they use resistors and no inductances to filter the voltage.

[harley92]

Thanks all for the advice.

I have another 37-620 code 125 but with the same speaker and field coil. I measured the voltage across the field and it averages around 22 volts. I calculated the current using the 1140 ohms of the field and multiplied that time the 22 volts and came up with about .45 watts. that seems low. To be on the safe side, I will try a metal film 1140 or close standard value 5 watt resistor and change the value of the second cap as suggested in the first post. Am I on the right track?
Thanks,
Gerald

[morzh]

Try music at the max volume.

[harley92]

I will try that and check the voltage. This radio does have very high volume when turned up.
Thanks