[Milsurplus] [Boatanchors] Carbon Mic Rejuvination

[C.Whitaker]

de WB2CPN Again,
In Germany 1946 and after I saw their broadcast quality
carbon mikes.
They were large, made from a 4 by 6 inch, or larger, piece
of 1 inch thick ceramic.  These were hollowed out about
3/8 inch deep, (1/4 inch edges), and filled with granular
carbon.  Two flat electrodes were glued into place side
by side before the carbon was poured in.
Then a removable cover made of thin plastic, or mica, was
fitted on to the top.  The mic was stood on its edge, and
I suppose the vibrations caused by the sound made the
resistance of the carbon vary.
Trivia, but from time to time the broadcast engineer would
remove the front cover, and regrind the carbon granules.
They developed a better mic, the condenser mic, which
had a vacuum tube amplifier close by, and was the 4 by
10 inch tube that you saw on the old German pre-WW II
propaganda films.
The "Western-Electric Approved Method" .pdf I got
some place recently summarizes:
1.  Connect the element to 6.3 VAC, 60 cps, through a
500 Ohms 1 Watt resistor.  (They call this the Bias Current.)
2.  With the bias applied, hold the element in the vertical
plane.
3.  For approximately one minute repeatedly rotate the
element +/- 120 degrees around its horizontal axis.
4.  Do not strike or tap the element. Do not allow the
element to overheat.  (What do they mean, overheat?)
5.  Then, for approximately 1 - 2 minutes "Blast" the
element with acoustic white noise, and if white noise
is not available just blowing into the element will work.
6.  This procedure may be repeated 2 - 3 times.  If the
element still has low output, excessive distortion, or
popcorn noise after several attempts, it should be
discarded.   (I never knew that Ma Bell ever discarded
anything, I put 22 years with AT&T Long lines.)
73  Clete
++++++++++++++++++++++++++++++++++++

On 3/16/2013 2:25 AM, Richard Brunner wrote:
> Modulating spark transmission has been done.  You have to get the 
> pulse rate/buzzer up high enough.  It sounds pretty good, but there is 
> a loud buzz and rushing noise in the background.  It was judged not 
> satisfactory.
>
> A carbon mic in the antenna lead works good, but beware of RF burns on 
> your nose.
>
> Richard, AA1P
>
>
> On 03/15/2013 10:44 PM, COURYHOUSE at aol.com wrote:
>> the only thng that  sounds  worse is  when you try to  modulate spark 
>> this
>> way
>>     In a message dated 3/15/2013 7:41:32 P.M. Mountain Standard Time,
>> w7qho at aol.com writes:
>>
>> Technique used in the very early days for some of the first voice  and
>> music transmissions....
>>
>> Dennis D.   W7QHO
>> Glendale, CA
>>
>> *************
>> On Mar 15, 2013, at 3:50 PM, Rob  Atkinson wrote:
>>
>>> you can put a carbon  mic in series between  the rig and antenna and
>>> use it to modulate the RF.    Supposed to work but sounds really bad.
>>> Only a few watts I  guess.
>>
>
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