[Milsurplus] BC 191 info needed

[Jack Antonio]

Hello Mike and the group

I put a BC-375 on the air about a year ago, and need to find the
time to get it back on the air, and here is what I found.

Before starting at all, I would highly recommend getting the manual
and studying it closely so you know how the transmitter is supposed
to work,. how the transmit/standby switching is accomplished, and do 
ohmmeter checks to make sure the relay contacts are clean etc.

Also, remember that the transmitter runs 1000 volts of plate voltage,
and in the BC-375 at least, the dynamotor runs continously, even
when the transmitter is not keyed, so be careful, think about what
you are doing and stay safe.

First, make sure all the power resistors in the back have continuity. One
of the resistor in mine had opened up, probably due to corrosion. Also
check the tube sockets, the contacts in mine had developed a sticky
grunge and had to be cleaned with silver polish.

Second, check all your fuses. They have a history of opening up with
age.

Third, if you have a dud 211 in either the oscillator or PA position, the
transmitter will draw lots of plate current, as the biases for all the 211 tubes
are derived from the grid of the PA, with no drive from a dead oscillator
there is no bias and hence lots of plate current.

Fourth.  The 3 section can type capacitor has a history of going leaky
and burning up.  Check it in yours, sorry I can't remember the circuit designation
and don't have time now to paw through the library.

Fifth. I ran mine at about 90 watts out on 80 and 75 with no problems.
I ran the transmitter into a coax fed resonant dipole through a 100 pf transmitting mica.
Remember these transmitters were designed to feed capacitive antennas, so give
it what it wants to see and it will be happy. I haven't tried mine out on 40 or 160 yet.

Sixth. The neutralization adjustment is very critical for good AM and minimum CW chirp.
I adjusted mine looking at an FM service monitor and adjusting the neutralization cap
for minimum FM. This was a two handed operation-one hand to adjust, and the other
to keep the transmitter on the test frequency. However I think you could adjust the
cap by listening to the transmitter on an AM receiver set to a narrow bandwidth, say
3 kc or so, and adjusting for best sounding AM.  

Hope all this helps!

Jack

Jack Antonio WA7DIA
scr-287@sbcglobal.net







> Hello from Down under ,
>                        As I mention the BC 191 I can hear people cringing in
> pain and running for cover .
> 
> I wonder if anyone has experience of using the BC 191 on the air , is it a
> useable set ? e.g. is it stable enough for the lower ham bands 80/40 .
VK3CZ