[Milsurplus] BC-221

Mon, 15 Dec 2003 13:36:18 EST

Ray,

All BC-221's except for the TS-164 variant were battery operated until the 
RA-133 and PP-79/UR came out.  The B-battery supplied 135 volts (when it was 
new, of course).  If there is a hole in the side of the case, someone may have 
drilled it as I don't recall there being any on the side or rear of any of the 
several dozen I have.  The RA-133 was intended to be operated with the back 
door open.  The line cord has a little box at about the midpoint with ON/OFF and 
STANDBY switches and an indicator lamp.  When I used to buy BC-221's all the 
time, one of the first things I always did was open the front door and sniff.  
If I smelled overheated or burned transformer insulation, I knew without 
looking further that it had had an AC supply, probably home-brew, and that it had 
been operated with the back door closed.  Further evidence could usually be 
found by noting a hole or notch hogged out of the back even if the supply was no 
longer present.

The RA-133's use an 0D3/VR-150 and a dropping resistor (2700/1W I seem to 
recall).  I noticed a slight shift in variable oscillator output frequency in 
some of mine when switching from cal or xtal to operate.  So I paralled the 
resistor with a 14 volt 1W Zener diode to stiffen the regulation and the shift 
pretty much went away.  However, as the original setup with batteries was expected 
to work over a reasonable percentage of the useful B-battery life, it should 
work fine @ 105 volts if you build a supply from scratch.  I didn't just swap 
the 0D3 for an 0C3 in the RA-133's as that would have required changing the 
regulator dropping resistor.  It was much simpler to tack the Zener in.  I used 
14V instead of 15V because the readily available 1N4700 series skipped it.

In a message dated 12/15/2003 11:39:09 AM Central Standard Time, 
[email protected] writes: 
> One thing always leads to another, although I have radios that are
> accurate to within a few cycles on the other side of the room, the back
> side of the room is where the tube radios are located, am practicing a
> strict policy of segregation- tube radios in one location, transistor in
> the other. so in running a TCS transmitter along with a HRO receiver the
> first thing you find is that you have no idea what frequency you are on.
> the solution is a BC-221, had one in the back and cleaned it up but have
> to build a AC power supply. the schematic calls for 135 Vdc, I am
> assuming that it will need to be regulated. was the stock internal power
> supply regulated? I was thinking of using a 0C3 or a 0D3 the problem
> being they are 105 or 150 volt tubes, will the unit work well on 150 Vdc
> or should I use a voltage divider with a 105 volt tube on the end to get
> my 135 Vdc? or just operate the meter from 105 Vdc? is the little hole
> on the side of the case for the power cord to exit? and last but not
> least has anyone had any success changing the plastic window over the
> book, looks like I may have to drill out the rivets that held in the old
> plastic. already striped , cleaned and painted the case but have no idea
> yet on replacing the plastic.
> 

73
Robert Downs - Houston
<http://www.wa5cab.com> (Web Store)
<[email protected]> (Primary email)
<[email protected]> (Backup email)

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