[Milsurplus] BC-223

[W7QHO at aol.com]

In a message dated 5/15/06 1:12:18 AM, w1eof at hamnutz.com writes:


> Does anyone have a manual, or at least a good readable schematic of a
> BC-223 transmitter?
> 

Mark,

I have a manual for the SCR-245 of which the BC-223 was the major component. 
Can supply you with a schematic.

There were a couple of different versions of this set, the BC-223-A which ran 
off 12 vdc only and the 12/24 volt BC-223-AX.   Wonder which one you're 
getting.   The companion receiver was the 
BC-312 and there were two 24 volt versions of this receiver which went with 
the 24 volt transmitters.   These receivers, the BC-312-MX and BC-312-NX are 
very rare but (strangely) the 12/24 volt versions of the transmitter are not.

I recently got a BC-223-A up and running for an exhibit at the Ft. MacArthur 
Military Museum in San Pedro, CA.  Some strange design choices in this rig 
such as the use of 20 watt WW resistors in circuits where a one watt unit would 
have been conservative.  When I first fired it up the set modulated 100% 
negative but only about 40% in the positive direction.   Found the grid bias way too 
low on the speech amplifier tube, a type 46 which is a big old glass tetrode 
with a 2.5 volt directly heated filament.   The tube is triode connected with 
second grid tied to the plate in this circuit.   Bias is derived from a tap 
off the PA grid-leak.   Took out the fixed resistor string and put in an 
equivalent pot (15K) which allowed adjustment for a symmetrical speech waveform.   
The modulator uses two more 46's with the two GRIDS tied together which makes 
the tubes zero bias triodes.    These old jugs are all operating with 500 volts 
on the plates, about 25% more than published specs call for.

The oscillator (801A) can operate either self excited or crystal controlled.  
 Much more output self excited and when running off a crystal there really 
isn't enough drive for the PA, especially on phone.  
Also, the use of a low amplification factor triode running on high plate 
voltage results if very high crystal currents.   Fortunate,   the oscillator is 
sufficiently stable for ham use in the self excited configuration.   

In common with other MOPA rigs (ex., BC-374, GP-7, ARC-5 and SCR-274, etc.) 
the set FM's on phone.   Not bad enough to be a problem on 160M (more on this 
below) but noticeable on 75. Responds well to the trick of slightly over 
neutralizing the 801A PA, though.   Can provide further details on this technique if 
you would like.

There were three tuning units for this set, the TU-17-A (2000 - 3000 kc), 
TU-18-A (3000 - 4500 kc) and TU-25-A (3500 - 5250 kc).   The TU-17 can be 
adjusted to cover most of 160M by closing up the internal osc. and PA padder caps.   
Both the '18 and '25 cover 75/80M of course.

Puts out a solid 18 watts of carrier on phone and modulates fully with good 
quality audio.   Quite stable when operating in the MO mode as mentioned 
before.   Fun little rig.

Hope this helps.

Dennis D. W7QHO
Glendale, CA