[Milsurplus] BC-230 / BC-430 Tube Substitutions

[David Stinson]

The BC-230 transmitter (part of SCR-183) 
and the BC-430 transmitter (part of SCR-283)
uses some expensive tubes, so a lot of them sit 
on the "get 'round 'tuit some day" shelf.

Awhile back, I tried substituting cheaper 6AQ5s.

http://home.netcom.com/~arc5/IMG_0934.JPG

Connections:
Triode Pin to 6AQ5 Pin
2 to 5,6  (Plate/Screen)
3 to 7  (Grid)
1 to  2,3  (Heater/Cathode)
4 to 4  (Heater)

The BC-230's four tube fils are wired in series/parrallel,
one RF tube and one MOD tube in each string.
The BC-430's fils are all in series.

I had a BC-430 on the bench.  I wired-up two 
Tungsol 6AQ5s in the RF sockets and jumpered-out
the two modulator sockets, then fed 12 volts to 
the fils.  and 300 volts B+.  The RF stages neutralized
fine and performed well with no problems at all.

Tonight, I put the two substitute 6AQ5 tubes
in the BC-230.  You can't sub just the modulation 
stages or just the RF stages because the fil. currents
for the original tubes vs. 6AQ5 don't balance.  
However,  you can sub one on each side, 
so the VT-52/VT-25 is on one fil. buss 
and the two 6AQ5s are on the other.
I subbed them onto each buss and tested.
The transmitter worked and modulated just fine.
In fact, the 6AQ5 as PA delivered 
a half-watt more power out.
This is pushing a 6AQ5 a little.  
I'm going to try tougher 5763s later.
When I get a chance, I'll build-up two more subs
and go with all four tubes as 6AQ5.

73 DE Dave AB5S.