[ARC5] [Milsurplus] Smart People: BC-9A Opinions Needed

[J Mcvey]

Sure enough there is -20V on the "low side of the  antenna! 
It's not entirely clear where S1 , connected to the + side of the battery connects via r3
Looks like it is the adjustable bias supply for the tubes but that schematic needs a MAJOR re-draw!The final plate is supplied 120V through the meter.The key connects a cap connected to -40 (???????)The loop antenna must be of critical size because it appears to be the tank circuit!
Do you have one of these?COOL!!!It reminds me of the old turn of the century Western Electric stuff with the bayonet bases. 


 

    On Tuesday, January 3, 2017 1:45 PM, Kenneth G. Gordon <kgordon2006 at frontier.com> wrote:
 

 On 3 Jan 2017 at 9:51, David Stinson wrote:

> https://goo.gl/photos/RCMKFHrZKZBHoeLc7

Hmmm.....it looks odd, but I can't yet put my finger on what about it is odd. The main reason 
I think Niel is wrong about the 120 V source is that the positive side DOES feed the plates 
through R-5 and the primary of T-1 and the two antenna coils, and the original schematic, or 
what's left of it, shows the minus sign at that point.

There is a more-detailed description on this site:

http://www.radiomuseum.org/r/wireless3_radio_transmitter_and_receiver_type_bc_9a.html

And there is a complete schematic shown on that page. However, the resolution of the .JPG 
there is so poor that no amount of messing with it can make it clear enough to see the 
details.

>From my looking at it until my eyes water, it looks as though your reconstruction of the 
schematic you have drawn is very close, if not completely accurate.

Surely, there must be someone somewhere who has one of these units and can give you 
better details. One was sold recently on eBay. Perhaps you could contact the buyer and get 
the necessary info from him?

> 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

Yes.

Ken W7EKB

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