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

Sun May 29 22:32:20 EDT 2016

Wonder what the magic N-1's resistance looks like when it's being excited or tapped?

 Wayne
WB4OGM

-----Original Message-----
From: David Stinson <arc5 at ix.netcom.com>
To: milsurplus <milsurplus at mailman.qth.net>
Sent: Sun, May 29, 2016 7:50 pm
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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