[Milsurplus] SIMPLE Carbon Microphone Substitute.

[antqradio at sbcglobal.net]

Probability a bit late to mention this but has anyone tried putting the carbon mike element in a vacuum for a day or so to get the moisture out?
Jim


      From: David Stinson <arc5 at ix.netcom.com>
 To: milsurplus at mailman.qth.net 
 Sent: Monday, May 30, 2016 5:35 PM
 Subject: Re: [Milsurplus] SIMPLE Carbon Microphone Substitute.
   
The Latest, 30 May 16

First, for the people who asked for the BC-669 
modulator diagram:

https://goo.gl/photos/2mjsnU8e1mLoVQG56

I did get around to working with a "Lo-Z,"
near-dead N-1 carbon mike element. 
Ohmmeter says about 225 Ohms.
No amount of bashing, baking or bouncing off walls
will get this element to modulate any of my many WWII 
milradio sets beyond about 20% at best.
So I scratched my head and did this:

https://goo.gl/photos/JX9WcN3PdMosA2De9

And it works! In fact, it will over-modulate the 669
if I close-talk it. Built it on a little board, mounted 
it on the back of the N-1 element and into the old 
T-17 case it goes.

https://goo.gl/photos/Cy7HLn6KWFikyZr77

The transistor- Remember way back in the 70s 
when mail-order surplus houses used to sell sacks 
of 100 "unmarked" or house-marked transistors? 
Well I've had some all these eons. I used a 
Sencore TS139 Beta tester to pick a couple
with betas over 100 (the 2N3569 and 2n2222 are
about 60 and 70 on the test set). So I don't know
what transistor this is, but there are lots of smart people
here who can suggest a good general-purpose NPN
with a 100+ Beta that will do Vcc of 40 or 60 at a 
few mils. There are likely dozens of them.
This is fun.

73 DE Dave AB5S
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