[Milsurplus] DAV-2 On Off Wiring

[WA5CAB at cs.com]

While having my second cup of coffee, I copied the DAV-2 schematic and 
"rewired" it to eliminate having to trace through four connectors.  You're 
correct that the mic voltage is 6 volts.  Not 1.5 as I think I said earlier.  The 
-4.5 V to ground is also applied to the modulator tube grid.  But the 
series combination of headset and audio transformer secondary is tied to the 
series combination of "A" battery, "C" battery, Mic and Mic Transformer primary 
at only one point.  So although the headset and transformer secondary are 
1.5 volts above ground, there is no mic current flow other than through stray 
capacitance and insulation leakage resistance.  Which when new would have 
both been pretty small (or large).  

So we're back to them using the switch terminal as a tie point and the wire 
from the switch to J401 for dual duty.

In a message dated 6/18/2010 5:30:14 AM Central Daylight Time, 
arc5 at ix.netcom.com writes: 
> I think it's "cheap and easy" sidetone, plus a way 
> to boost the carbon microphone voltage.
> If you follow the circuit out, the mike voltage is the 
> "C" voltage in series with the "A" voltage, giving 
> 6 volts for the carbon mike.  
> Also, the mike voltage gets tapped to the 
> headset, which has a potential difference between
> the two batteries, but no path to ground.
> So you get cheap sidetone.
> 

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