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Bernard Cleyet wrote:
Back in the middle ages I repaired radios for pin money. The "big"Carr's Old Time Radios! ...
ones often used a field coil instead of a PM in the loud speaker for
the voice coil "to work against" [correct physics expression]. The
coil did double duty as part of the filter for the HV supply. I
don't remember if they were L or C input filters, but either way I
was surprised -- no audible background hum; still am.
Anyone out there have an idea why.
bc
__
<http://books.google.com/books? id=KkvHhhJcGIwC&pg=PA101&lpg=PA101&dq=field+coil+in+loudspeaker+- +hum&source=bl&ots=gcw4lZ3ZKr&sig=Q47icOXJYINJP8PYWCk3qlGVBdM&hl=en&ei =l_v0ScPaGpTcMbe- sKkP&sa=X&oi=book_result&ct=result&resnum=2#PPA101,M1>
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*http://tinyurl.com/c3lu9x*