[GreenKeys] WU M21-A (was Western Union tape transmitter 22-A by J H Bunnell)

[Jim Haynes]

On Mon, 2 Feb 2015, Jeffrey D Angus wrote:

> On 2/2/2015 9:06 AM, Duncan Brown wrote:
>>  There is an article in the April 1962 issue of RTTY magazine that has
>>  an electronic distributor for the WU M21-A.
> Oh this is absolutely precious.  24 tubes. It would be even more if it
> wasn't for the 6SL7 dual triodes and 6H6 dual diodes.
>
And if you should be so foolish as to attempt to build the circuit...
There was an error in the schematic - I don't recall offhand if the
1962 reprint has it corrected.  Also as I recall W6ZBV later replaced
the 6V6 and millisec relay with a 2050 thyratron..

I actually built the circuit, but never got it to work.  Didn't know about
the schematic error.  Was using junk-box pots.  Had no means of testing
and adjusting.  Well if I had been smarter I could have built a
multivibrator that would be adjustable to the various pulse lengths,
but then I didn't have a calibrated triggered sweep scope to set it with.