[Milsurplus] TCS

[W7QHO at aol.com]

In a message dated 7/3/06 10:20:15 AM, scottjohnson1 at cox.net writes:


> The RS-38 was also a standard civil general aviation and large aircraft
> standby mic up through the mid sixties.  It is as reliable as a WeCo
> handset mic, but with radios such as the TCS, there just isn't quite
> enough gain in the audio chain. I am surprised at Collins for not
> employing at least one gain stage in front of the modulators.  Even the
> BC-375 had a triode gain stage!
> 
> 

Didn't realize the RS-38 was so widely used.   Have accumulated a number of 
examples over the years and found the "working" percentage to be about the same 
as old T-17s.   Thing is, the TCS didn't really have an audio chain in the 
usual sense, just fed the mic through a transformer directly to the 
P-P 1625 grids.     Same thing in the BC-441 and in both cases, unless one is 
using a very hot mic, modulation is limited to around 50% at normal speech 
levels.   The BC-375 even with it's type 10 speech amp stage isn't much better, 
BTW.

I use a small transistorized mic amp to improve the situation in my examples 
of the above rigs.   Reversible mod, small enough to hide in a corner 
underneath the chassis and completely solves the problem.   Details on request.   

The military seemed to be satisfied with low (by ham standards) modulation 
levels during the WW2 period.   One has to yell into a normal T-17 to get 100% 
even with an originally wired ART-13.

I use a BC-453 "Q-5er" with my TCS receiver.

Dennis D. W7QHO
Glendale, CA