[Milsurplus] Aw Heck (Was: SIMPLE Carbon Microphone Sub)

[Mike Feher]

Dave -

If you are looking for more gain, you might want to play with a Darlington
configuration. 73 - Mike 

Mike B. Feher, N4FS
89 Arnold Blvd.
Howell, NJ, 07731
732-886-5960 


-----Original Message-----
From: Milsurplus [mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of
David Stinson
Sent: Sunday, May 29, 2016 9:50 PM
To: milsurplus at mailman.qth.net
Subject: [Milsurplus] Aw Heck (Was: SIMPLE Carbon Microphone Sub)

(I'm copying this to milsurplus only because it's  the only place anyone
responds so I assume these are the only people who read.)

Ya'll remember me telling you about this "magic" T-17 being stock?  I had to
know so I unsealed the screws.
It was black wax instead of the usual stuff, which gave me an "uh oh"
feeling right there.
I opened it and... It ain't stock.
Inside is an N-1 telephone element.
Glued to the microphone face.
And some stuffing.

Well... I did some research and found out exactly who did this.  I nailed
that evil-doer!
It was me.  In 2012.
Guys, I have NO MEMORY at all of doing this.
None.  Not a shred.  Yet there I am on qrz.com in October of 2012 talking
all about it.
Which wasn't that long ago.
Diabetes can cause early-onset dementia.
Frightening.   But at least that part of the 
"magical mystery T-17" is solved.
HOWEVER, the other mysteries remain.

I've checked this "magic" N-1 with my Fluke 8050A bench meter and my brand
new Fluke 77 hand meter.
Assuming I remember how to read them....
On both meters, it checks about 20K Ohms.
And it works spendidly on most of my mil-rigs.
I have another N-1, a T-1 and other various elements.
All read 60-300 Ohms.  None will modulate any of the rigs properly.  The
best of this lot is the large K1 transmitter element in the "candle stick"
microphone.  It measures 2K Ohms and will mod the rigs about half way if you
yell.
I see all your information.  I don't take issue with it.
I don't understand why this is happening.
It just is.

A dim light came on in what passes for my brain.
Take another look at the electret carbon mic replacement circuit:  
https://goo.gl/photos/26HUmzVuqhZKWrNZ7

This puts out nice-sounding audio and will modulate the rigs fully, but you
got to close-talk it.
I haven't tried another electret- looking for a higher- gain transistor
first.  2N2222 is a little better.

The circuit.... and a 2K carbon element...hmmm.
So I did this:
https://goo.gl/photos/6Ua2hJmLdSrkigw57

And "Ala-Kazam!" I got excellent-sounding, 100% modulation from a normal
voice using this very cool "candle-stick" mike.
Fortunately, the element in this mike
is isolated from ground.
And one less part, so
"The Law of Pernicious Parts Count" 
is being respected.
Put a little board right on the back of the element and away we go.
https://goo.gl/photos/Ce4RQuJGBY3WciBK9

Just to be through, I did try the Lo-Z elements ( Hey... Z=X+R, even when X
is zero).
and they did not work, as we would expect since they don't bias the
transistor properly and if you put them in series with a resistor, they
aren't a big-enough fraction of the total Z to matter.
I'm thinking of a proper bias divider and putting the Lo-Z elements in the
Emitter lead.
More than one way to skin a cat!

Will let you know if that works.  In the mean time, can someone tell me why
an N-1 element that measures 20K Ohms works so well??

73 DE Dave AB5S





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