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

[Duncan Brown]

Don,

There are not too many of the M21-A vintage units left, so it will be 
hard to find any parts.  They were designed around 1920 for Western 
Union Multiplexed systems (four circuits on one pair of wires) and were 
used up until the 1940-50s. (I'm surprised that Bul. 139 is dated Dec, 
1947, but apparently there were still systems using the equipment then 
and Teletype Corp. was still supporting them.)

The selector magnets were each pulsed and then mechanically latched into 
place until the unit received the print command. If you put in a piece 
of tape and a ribbon in the unit, you can press down on individual 
selector magnets to latch in a letter code, then press down on the print 
solenoid and print the letter on the tape.

To operate the older units with five selector magnets, you needed a 
serial to parallel converter  or "Receiving Distributor."  There is an 
article in the April 1962 issue of RTTY magazine that has an electronic 
distributor for the WU M21-A.  I can send you a PDF scan if you are 
interested.

The AWA Museum has a copy of the M21-A parts manual (Bul. 1027; March 
1947) which I can scan if anyone wants it.

Have fun,

Duncan
K2OEQ

On 01-Feb-15 14:12, Donald Lampert wrote:
> Thanks, Duncan for the WU info and photo, as I just got a WU 21-A multiplex tape printer from Lee Mushel. There isn't much online about these units, but I did find the manual for it at the navy-radio site.
> It needs the tape holder can from the right side, and most of the wiring and power cord are gone but the mechanics are cleaning up nicely - any idea where to get parts?
> Thanks, Don L
> --------------------------------------------
>


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