12" Philco field coil speakers - Printable Version

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12" Philco field coil speakers - Guest - 07-24-2008

I have been using 2 Philco 12" field coil speakers in a stereo sound system.
They both have 1000 ohm field coils or thereabouts.
I built a power supply to run them at 95 volts dc.
Am I in the right vicinity with the voltage?
These are really excellent speakers and I am running them fullrange.
Thanks for any suggestions.
Bill Larson

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- Raleigh - 08-19-2008

As a starting point we need to know what kind of radio those speakers came from. The designed voltage drop, current, and power dissipation could probably be calculated from data on the schematics.

I have worked on a Philco 41-280 with a 12 in, 1100 ohm field coil speaker and also some very similar other radios with 1100 ohm coils, but with smaller cones. If you are using a speaker from one of these or a similar radio, the following calculations should apply.

I calculate that these radios were designed to run around 66 milliamps through the field coil, which calculates to a voltage drop of about 72 VDC and power dissipation of about 4.8 watts. A year or so ago I measured the field coil current and voltage drops in a 40-150, which has a 1100 ohm field coil, and it matched the calculations pretty well.

Now, if you are dropping 95 VDC across two 1100 ohm coils in series, then you are running about 43 milliamps through them and dissipating about 2 watts each. On the other hand, if you are dropping 95 volts across each coil, then you are running them at about 86 milliamps and dissipating about 8 watts each.

Again, if your speakers are from a different radio, the calculations could be very different.

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