[BC] Old Speaker

[Harold Hallikainen]

> At 03:17 PM 11/25/2005, Glen Kippel wrote:
>
>>I just wanted to point out the field-coil caveat in case Stanley hooked
>> it
>>up and couldn't get anything out of it and wondered why.  It may need
>>something like 250 to 400 volts across the coil if it has one.
>
> Glen -


I think the field coil in those speakers was a few hundred volts above
ground, but the voltage across the coil was substantially less. The coil
doubled as a power supply choke in a pi section filter. I think they even
phased the coil so any hum left in the final audio on the voice coil was
cancelled by hum on the field coil. Those old radios had some neat tricks.
Some had 10kHz whistle filters. Some also had a shunt light bulb in the
audio to act as a loudness expander.

Harold

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