[Milsurplus] TCS: T-17 and RS-38 Microphone Mystery

[David Stinson]

Been refurbishing at TCS-13 (photo on my QRZ.com page).
I dug-out all my T-17s and RS-38s, looking to 
"separate the sheep from the goats." Most of these don't 
work with either SCR-274N or SCR-287.

To my great surprise, ALL of them work on the TCS
transmitter, the worst of the lot still doing at least 70%
modulation. Even an old Air Corps throat mike 
will do nearly 100% if worn properly.
The 274N and 287 use current-limited 
filament voltage to power the carbon mike.
The TCS uses the cathode bias of the modulators.
A diagram of the TCS modulator is at:
http://home.netcom.com/~arc5/tcsmod.jpg

So- why do they work with the TCS, 
but not with the other rigs?

73 DE Dave AB5S