[MRCA] BC-187 Transmitter Voltages?

[Bill W2DGB]

I wrote the receiver up for the AWA Journal Communications Receiver column a 
couple of years ago, based on my having had one years ago.  At that time I 
also had the associated matched modulator and tx, but unfortunately only the 
rx remains.

Anyway, I asked the same question in the article, why these archaic designs 
were still being produced in the 1940s.  One answer came back was to the 
effect that this little regen receiver, which works quite well, by the way, 
was the only radio that worked reliably in the jungles of Burma. I have no 
confirmation, but it is a good story, and does make some sense.

73,   Bill  w2dgb


----- Original Message ----- 
From: "Mike Morrow" <kk5f at earthlink.net>
To: "Military Radio Collectors Association" <mrca at mailman.qth.net>
Sent: Wednesday, February 28, 2007 8:07 PM
Subject: Re: [MRCA] BC-187 Transmitter Voltages?


> Breck wrote:
>
>>Can someone tell me what the  filament voltage and B plus requirement is 
>>for
>>the BC-187(SCR-175).
>
> That's the SCR-178, or when packaged for carry by mule-pack, the SCR-179.
>
> The following page has some info and a schematic:
>
> http://hereford.ampr.org/millist/m11.html
>
> Warning:  This page is wrong about the filament voltage.  It states it as 
> 1.5 volts, but both the VT-25 (type 10) MO and VT-55 (type 865) PA tubes 
> require 7.5 volts (DC) for filaments.  This page specifies 500 vdc for the 
> plate voltages, which sounds about right, but I've never tried to put my 
> SCR-178 on the air, and I don't have the hand-cranked generator that would 
> be the normal source of transmitter power.
>
> On the web page given above, you can also check out the associated screen 
> modulator (BC-188) and receiver (BC-186).  All three units, plus a battery 
> box for the receiver power supply, were packed in a fairly large chest 
> whose front opened and formed an operating desk, complete with a fixture 
> for holding the J-44 key.  Wiring to connect the units together was also 
> part of the chest.  The receiver was a regen with RF stage and audio 
> amplifier (three tubes).
>
> Why they were making these obsolete dinosaurs as late as 1942 is an 
> interesting question.
>
> Mike / KK5F
>
>
>
>
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