[ARC5] BC-230 / SCR-183 "Cheap Tube" Project Report.

[David Stinson]

The project to revive BC-230 / BC-430 transmitters
with affordable tubes and to crystal-control them without
hacking them up has gone well.  
Where some information conflicts with earlier posts,
this one supersedes.
http://home.netcom.com/~arc5/SCR-183/BC230s.jpg
>From left to right:
10109 KC Xtal CW (need meter and cover)
7040 KC Xtal CW
3890 AM MOPA.

5763 tubes:  I finally got these to work.  The fix was so 
obvious and simple I should have seen it at once.
A "gimmick" cap adding 2-3 pFd across the Neutralizing
cap and they tame as easily as the 6AQ5s. 

The only reason to change the bias resistors is if one 
wants to use the rig on AM phone with the cheaper tubes.
If only doing CW, keep the original 20K resistor bias set-up.
You don't need the MOD tubes if doing CW, but I did
install them in the two sets I use for CW to keep the filament
strings original.  The plates and grids are not connected.

Speaking of neutralizing: One neutralizing setting works for 
one coil set, but may not work for another, especially if you've
had to rewind an open Neutralizing coil.  A scope or a good 
RF probe on a meter is invaluable in neutralizing.

Xtal Control:
If you have a C-184 Xtal-Control coil set, it can be
"fudged" down to 75 meters without much trouble
but, if you have the 80-75 coil set and a proper 
power supply, the rig is plenty stable "as-is."
Putting the rig on 40-meters Xtal control requires
an FT-243 or bigger-blank crystal, a resistor, 
an RFC choke and either a 6.2-7.7 MC coil set 
or a "fudged" 5-6.2 MC set.  Little HC-25s will overheat.
Nice, solid chirp-free note on 7040 KC.

Here are the three "finished" sets.
If anyone wants details on how each was done, just write.
Output measured with a calibrated scope,
formula P =  ((Vp-t-p / 2.828)^2) / R 

75 Meters AM
BC-AH-230  Aircraft Radio Corp. Ser.#62
Order 11482-NY-36  Date 11-25-35
3890 KC. Original tubes (VT-25A, not the fake 801s).
3200-4000 KC coil set, MO tuning 2075.
100 pFd antenna series cap.  
ANT coil tap 8 turns from bottom.  4 Watts out.

40 Meters CW
BC-AL-230 Graybar Ser.# 44 (Thanks, Hue!)
Order 19070-NY-39 Date 6-20-39
7040 KC.  6AQ5 tubes.
6.2-7.7 coil set, FT-243 Xtal, Osc. shunt-fed.
MO tuning 1537.  100 pFd antenna series cap.
ANT tap 5 up from bottom.  7 Watts out.

30 Meters CW
BC-AL-230 Graybar Ser.#836
Order 19070-NY-39 Date 6-20-39
5763 tubes. 10109 KC Xtal via C-184 coil set 
5055 xtal doubled in final, PA/ANT coil rewound from 
a broken 4-5 MC PA/ANT coil, wound over the 
original coupling winding, 12 turns, PA tap at 
9 turns from the bottom,  ANT tap 6 turns from bottom.
50 pFd antenna series cap.  5 Watts out.
This one isn't really "finished."  It still chirps a little.
Don't have another crystal to test so 
going to try a programmable osc in place of it.

73 DE Dave AB5S