[Milsurplus] SIMPLE Carbon Microphone Substitute.

[Hubert Miller]

Hanging a lytic from base to ground would give you even more gain. 
Nice work, Dave, solving the problem.
-Hue Miller 

-----Original Message-----
From: Milsurplus [mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of
David Stinson
Sent: Monday, May 30, 2016 3:35 PM
To: milsurplus at mailman.qth.net
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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