Replacing a field coil speaker - Printable Version
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RE: Replacing a field coil speaker - DaleHCook - 03-29-2026
RodB Wrote: You will be removing the inductive part of the filter which does the biggest amount of filtering ...
That is why I incorporated an 8 Henry filter choke in my Universal Shop Speaker and Dummy Field Coil.
RE: Replacing a field coil speaker - morzh - 03-29-2026
If you can restore the speaker, it is a noble cause and is better than any replacement (I mean, all things considered; a modern speaker would sound better, but this is not the goal, right?) that is not original to the design.
After all this is what we are trying to do, preserving the technology, right?
RE: Replacing a field coil speaker - Chas - 03-29-2026
Quote:I haven't done this before, but it's time I figured this out. Not a Philco but a Fairfield Morse. As I understand this I replace the field coil (circled on schematic) with a resistor of the same value and high wattage and put a permanent magnet speaker where the speaker goes. There's a cap/resistor in series across the speaker which I assume stays. Am I missing something??Ummm, yes, the field coil is in the center-tap return of the power transformer. Its resistance in parallel with three other resistors sets up bias voltages for the radio. May, have to add filter caps to the bias as hum could appear because the lack of inductance for filter ripple. The 6L6 must have a near correct bias as it could draw considerable plate current bring down the total B+.
Yes, follow advice for the speaker repair in ARF. I, had to make a jig for a 12" speaker to correctly align the voice coil to the new cone. Made the jig from a PVC pipe, fittings and a base of MDF.
GL
Chas