Philco 20, 70, or 90 field coil impedence? - Printable Version
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Philco 20, 70, or 90 field coil impedence? - catman351 - 06-19-2017
Hi:
What is the impedance of the field coil for the above speakers? I'm thinking about substituting the field coil in the power supply for an equivalent choke. I'm trying out a different audio output circuit using a PM speaker. Thanks. Cal.
RE: Philco 20, 70, or 90 field coil impedence? - Nathan Slingerland - 06-19-2017
Welcome to the Phorum Cal!
This tech article has lots of info on the Philco 20/70/90 speakers:
http://philcoradio.com/phorum/showthread.php?tid=14991
RE: Philco 20, 70, or 90 field coil impedence? - catman351 - 06-19-2017
Thanks. There are resistance readings for the field coils.
However, there are no inductance values.
RE: Philco 20, 70, or 90 field coil impedence? - Radioroslyn - 06-19-2017
That question came up a number of yrs ago. Best I remember it was something like 37H but that was with no current flow though it. I would suspect that it going to be somewhat less. The hard part is going to find a choke a dc resistance that is close to so your voltage drop across it will be similar. There was a thread about how to rewind the old coil. On most those early K style spkrs the fc is bolted in so It's not rocket science to remove it and rewind.
ps I think you mean inductance rather that impedance.
RE: Philco 20, 70, or 90 field coil impedence? - morzh - 06-19-2017
tom-eight-o - tom-ah-to.
RE: Philco 20, 70, or 90 field coil impedence? - catman351 - 06-19-2017
You are correct. Inductance.
RE: Philco 20, 70, or 90 field coil impedence? - Radioroslyn - 06-19-2017
I suppose in the big scheme of things what I would look for is a 10-20H choke at 40ma or better. Since it's in the HV side rather than the bias the resistance isn't super critical but will have an effect on the amount of HV. A series resistor is probably a good idea to equal out the total resistance to the original. Would keep the input capacitor at the same value but if hum is an issue then increase the size of the output capacitor.