[Milsurplus] TCS Audio

[WA5CAB at cs.com]

Group,

There's nothing unusual about low power transmitters of the era having no 
speech amplifier tube between the microphone transformer and the modulator 
tube(s).  More didn't than did.  Six more examples are BC-474, BC-654, BC-1306 and 
all three of the Command Set modulators.  The only significant difference in 
this regard between the TCS transmitter and the MD-7/ARC-5 is the microphone 
bias resistor, and that's because the TCS was 14 volt and the MD-7 28 volt.

On the other hand, the BC-625, which probably didn't need it, did have a 
speech amplifier tube.

In a message dated 7/3/2006 2:18:34 PM Central Daylight Time, W7QHO at aol.com 
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.

Robert Downs - Houston
<http://www.wa5cab.com> (Web Store)
MVPA 9480
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