[GreenKeys] Current limiting

[Jim Haynes]

As others have explained, there is a series resistor of about 2000 ohms
to limit the current to 60ma, and incidentally to reduce the time
constant caused by the inductance of the selector magnet, t=L/R

Teletype did like ferroresonant transformer power supplies, but I don't
know what current they limit at.  Something more than the rated output
of the supply.  And of course those can only be used where the power
frequency is fairly accurate.




jhhaynes at earthlink dot net