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RE: Field coil dummy...

In most vintage radios (consoles from the 1930s, for example) the field coils are indeed doing double duty as the magnet for the speaker and the choke for the power supply. The voltage may be as high as 300vdc so do beware. Sometimes the cone of the speaker gets damaged, in which case the suggested "keep the coil and use a permanent magnet speaker" approach works well. However, often the field coil itself fails due to aging and heat fatigue, or from failure modes in the radio/amplifier that caused high current draw. In that case you are kind of SOL. The coil in the field coil speaker cannot be easily repaired and I don't think anybody makes replacements.

Supposedly, field coils can create a stronger magnetic field than typical magnets, and therefore a better speaker. I have some doubt about this basic tenant though. A very powerful speaker magnet could be made with neodymium magnets, but I am not seeing such items in the marketplace.


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