[Milsurplus] Smart People: BC-9A Opinions Needed

[Al Klase]

Dave,

An interesting project you have there.  The original manual is now on my 
site:  http://www.skywaves.ar88.net/mil/SCR-77/SCR-77.html (Compliments 
of the Steve Rosenfeld.)  It includes a schematic and circuit analysis.  
The loop antenna is the inductor in the single tuned circuit.  The 
oscillator / detector runs on the same frequency on both transmit and 
receive, and depends on the signal from the other set to produce a beat 
note in the headset!

I appears this circuit was based on suggestions from Edwin Armstrong 
when he was attached to the Signal Corps Division of Research and 
Inspection in Paris in 1918.  There will be more on that on my site when 
I get my story straight.  I put some of the source documents at the 
above link.   Any input greatly appreciated.

VY 73,
Al

On 1/3/2017 10:51 AM, David Stinson wrote:
> Good morning.  There's precious little specific information technical 
> on the WWI-era BC-9A
> (SCR-77A) battery-operated, portable CW set.
> Some general descriptions but no clearly-copied schematic.
> https://goo.gl/photos/uVYek56Zoja1jqQq6
>
> There is a schematic on the inside of the cover, but mine was stained 
> and missing a large part
> of the center of the diagram.  I have worked with what I could find to 
> re-create the diagram.
> Please look at this photo.  The re-created part
> is in the green outline.  It is close to the smeared,
> obscure copies I've seen but not certain.  Does
> this circuit make sense to you?
> https://goo.gl/photos/RCMKFHrZKZBHoeLc7
>
> Next:  I'm working on power supply solutions
> (other than the obvious batteries.)  I need to do some RF bypassing in 
> the supply lines and need
> a point I can call "Ground" in this circuit.
> This diagram- Red lines appear to me to be
> what one would think of as "RF Ground," while
> the 120 and 40 B- lines reference in green.
> That puts B- above the "RF Ground" by the filament bias, adding to the 
> grid bias on the tubes.  Do you think my analysis of
> the red line being the place I could think of as "Ground" is sound?
> https://goo.gl/photos/bucwyMuC12jdfWWT7
>
> Thanks for your input and prosper in 2017.
> 73 DE Dave AB5S
>
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-- 
Al Klase – N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net/