[GreenKeys] TTYs in news service

[John Nagle]

> A normal loop consists of 120 to 150 volts with a 10 kilohm 20 watt  
> resistor (adjustable) in series with the loop and selector magnets.   
> Just enough voltage to get 60 ma through only the selector magnet  
> resistance is not going to work.

No, it's a 2K resistor.  10 watts is sufficient.

R = E / I

E = 120V
I = 0.060A
R = 120 / 0.060 = 2000

W = E * I

E = 120V
I = 0.060A
W = 7.2W

Here's the schematic for a Model 28, with a built-in 135VDC supply
in series with a 2K ohm resistor to power its own selector magnet.

http://207.207.72.42/development/teletype/model28ASR/m28-13.gif

Can you be more specific about what you've got?  Many Model 28
units come with a power supply, and should be able to loop back
in echo mode without external gear.

				John Nagle