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

[antqradio at sbcglobal.net]

I thought about the carbon microphone current bias too but I figured that the cathode bias voltage would be lower then the filament voltage assuming (here we go again) that filament voltage was 28 volts.  My thought was that the transformer turns ratio was high enough to properly drive the modulator tube grids, i.e. tens of volts.  I have gone no further then make a guess that this is the case so I could be way off base.



      From: "WA5CAB at cs.com" <WA5CAB at cs.com>
 To: antqradio at sbcglobal.net 
 Sent: Monday, December 21, 2015 11:46 AM
 Subject: Re: [Milsurplus] TCS: T-17 and RS-38 Microphone Mystery
  
Better yet, what is the microphone bias voltage under modulation versus the voltage at the same point in the other rigs?

In a message dated 12/21/2015 10:46:34 AM Central Standard Time, antqradio at sbcglobal.net writes: 

What is the turns ratio of T-101 versus what is used in the other modulators?


From: David Stinson <arc5 at ix.netcom.com>
To: mrca at mailman.qth.net; milsurplus at mailman.qth.net 
Sent: Monday, December 21, 2015 10:21 AM
Subject: [Milsurplus] TCS: T-17 and RS-38 Microphone Mystery


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







Robert & Susan Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480

   

  
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