How To Use A Field Coil Speaker Alone

[Carl WA1KPD]

I have a nice old large field coil speaker I would like to use in the station. I have some good variable ta xfrmrs so speaker impedance is not a problem.
I know the field coils act as a choke for power supplies but I want to use it with different radios. Any thoughts on the best way to supply the voltage for the coil that is art of the speaker cabinet?
Carl
/KPD

[WQ9E]

Carl,

Do you know what radio this came from?  You can work back from that to get the voltage/current the field coil originally saw.

You can probably get away building a line operated supply (transformerless, possibly a voltage doubler) into the speaker cabinet with a series resistor to set the current.

[Opcom]

A relatively low voltage is all that is needed for most of them, maybe 20-60V. You have the opportunity to make it well filtered, possibly unlike in the original application.

These things only get slightly warm and maybe you can set the current for a small rise. Knowing resistance and if you can determine the wire gauge, that may help set it up more scientifically.

The loudest or best sound is not always made at the highest magnetic field. Unless it is tiny, you can't go wrong starting at 50mA so try it and you may be satisfied.

Consider the draw of a pair of commonly used class A push pull tubes of those days, like 2A3's, 6B4's, 42s, 6K6s, 6F6s.