[GreenKeys] Western Union Ticker-5A Stock Quotation Machine

[WA5CAB at cs.com]

Brooke,

This has been discussed (and cussed) here several times in the past year.  
But the short answer is that if you run the loop from say 24 VDC, which is high 
enough to put 60 mA through the selector magnets (usually, anyway), the 
current rise time when going from Space to Mark is so long that the Selector Range 
goes to zero.  And the error rate goes sky high.  When you run 115 VDC and an 
adjustable resistor, the resistor swamps the inductance and you get nearly a 
square wave (current) through the magnets.  And the machine is happy.  

Historically, 115 VDC was chosen because some of the motors were 115 VDC as 
well.  So you could run the entire machine from one generator.

In a message dated 4/17/2007 4:34:09 PM Central Standard Time, 
brooke at pacific.net writes: 
> Why do teletype machines typically have loop voltages in the 100 to 200 
> volt 
> area?  Could these be replaced by current sources that have a voltage 
> compliance a litter higher than the voltage drop across the input relay 
> coil?

Robert Downs - Houston
<http://www.wa5cab.com> (Web Store)
MVPA 9480
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