[GreenKeys] Interesting cipher machine.

[Jim Haynes]

I don't believe the part about the synchronous motor is correct.  All the 
31s I have seen in Western Union carrying cases have governed motors, but 
that's not many machines.  But the real reason for my disbelief in the 
sync motor is more convoluted.  I have somewhere a copy of Teletype 
instructions book, and one of the instructions is how to fill out a form 
for an R&D development case.  And for an example they happened to choose a 
case to put a sync motor in a Model 31.  (Which suggests some customer 
wanted it that way)  The example form says something about they couldn't 
get a sync motor with enpough starting torque to fit in the space occupied 
by the governed motor, so it was going to take more money to get a
workable sync motor option.

The motor in the airplane version was actually a dynamotor.  Governed
motors tend to generate a lot of RF noise, so in that version they used
a vacuum tube to control the current to the motor.  Then the governor
contacts had to handle only the tiny current to the grid circuit of the
tube.  And the dynamotor allowed the machine to run on 28VDC airplane
power.


On Fri, 11 Feb 2022, Duncan Brown wrote:

> Teletype Corp later came out with a version with a synchronous motor and a 
> carrying case and sold them to Western Union, who leased them out to sports 
> newsmen.  They took them to games and typed out the game, play by play.
>