[Milsurplus] SIMPLE Carbon Microphone Substitute.

David Stinson arc5 at ix.netcom.com
Sun May 29 06:22:45 EDT 2016


Guys, I understand and of course, your points are well-taken.
One nice thing about saying something that seems 
outrageous:  You know for sure that *somebody* is
actually reading what you take the trouble to write ;-D.
At least on the milsurplus list.

I have several carbon microphones.  I have one unmolested
T-17 that gets excellent audio reports and provides 
full modulation on both the BC-669 and the SCR-274N.
I've metered the element repeatedly.  
It reads in excess of 20K every time.
I don't get it, either.

Several other elements I've tried on the 669 measure low 
values (under 200 Ohms) and none of them will modulate
the rig beyond about 20%.  And they sound bad.
I decided to make the carbon element subber so I could
use a "candle stick" mic I have that, no matter what I did
including installing a NOS element, pounding it, heating it,
praying etc. would not fully modulate any of my rigs and 
sounded like doggie doo anyway.  The candle-stick 
mic will look awesome with the rig if I ever do another
display somewhere.
The sweet-sounding T-17 is in original condition with
still-sealed screws and original cord.  
IIRC it's a 1943 contract and is the usual "three-holer."  

I can't explain it. I just report it. 
I wish someone would explain it to me.

73 DE Dave AB5S

P.S. I did try the little subber with bypassed emitter bias
and the large base-to-ground resistor you'd expect.
It resulted in about half the output and no change in
audio quality.  Again- I don't explain it, just report it.
Can someone suggest a transistor with more gain
than the 2N3569 in this application?






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