[Boatanchors] Carbon Mic Rejuvination

[J. Forster]

Richard,

More correctly, carbon mikes are 'energy modulators'- they modulate the
flow of electrical energy in response to a mechanical input...  very like
a valve for water.

They DO have power gain, as do valves for water or air.

Best,

-John

===============



>
> ----- Original Message -----
> From: "Jim" <jbrannig at verizon.net>
> To: "Charlie , W5COV" <cvest at cox.net>; "milsurplus QSLNet"
> <milsurplus at mailman.qth.net>; <grc-9 at yahoogroups.com>;
> <boatanchors at mailman.qth.net>
> Sent: Saturday, March 16, 2013 5:20 AM
> Subject: Re: [Boatanchors] Carbon Mic Rejuvination
>
>
>>I recall a telephone repairman WHACKING a handset on a desk
>>to loosen the carbon granules in the microphone.
>>
>> DON'T try this on a modern telephone!
>>
>> Jim
>
>      Many carbon elements are subject to "packing" of the
> carbon granules, when banged or shaken hard the granules are
> separated again.  The vulnerability to packing depends on
> the mechanical design of the carbon chamber and to the
> condition of the carbon. Many mics are also position
> sensitive.  The Western Electric T-1, used in the 500 series
> phones, was designed to avoid both problems.  I don't know
> what WECO did to process the carbon to eliminate packing the
> carbon chamber is designed so that the overall contact of
> carbon to metal remains fairly constant with position.  The
> old carbon mics used in early broadcasting were very
> temperamental and often packed.  Packing can also come from
> excessive current.  In general, the current through the
> carbon should be the minimum that will produce sufficient
> output.
>      Carbon microphones are actually amplifiers; the output
> is from a source external to the microphone rather than
> being directly absorbed from the airborne soundwaves.  It is
> this amplification that resulted in the universal use of
> carbon microphones in the telephone system for nearly a
> century.  When small, efficient, amplifiers became available
> carbon elements were pretty much replaced with electret
> mics.  The electret itself is an interesting development, a
> condenser microphone which does not need an external source
> of bias voltage. In combination with solid state amplifiers
> they pretty much eliminated the use of carbon elements for
> most applications.
>
>
> --
> Richard Knoppow
> Los Angeles
> WB6KBL
> dickburk at ix.netcom.com
>
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