[MRCA] BC-187 Transmitter Voltages?

[Mike Morrow]

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