[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 
"seperate 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.   The 274N and 287 use current-limited 
filament voltage to power the carbon mike.
The TCS uses the cathode bias of the modulators.
Diagram attached.
So- why do they work with the TCS, but not with
other rigs?

73 DE Dave AB5S
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