Foxs Mercantile wrote:

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On 11/2/2017 8:25 PM, Clifford Heath wrote:
Also... as a filter in the power supply? Because yeah,
the one place you really want all that filtered-out
100Hz energy is in your speaker Or perhaps it was
arranged so that enough got through to the amp to
cancel it out? Crazy stuff anyhow.

Electro-dynamic speakers had the filed coil which
doubled as the power supply filter choke.
Alon with the voice coil, there was a hum-bucking coil
that canceled the residual hum from the field winding.


** See link for discussion and details of ED speaker background hum.


https://www.radiomuseum.org/forum/ba...peakers.ht ml


...... Phil