[GreenKeys] Printer over the phone lines.

[Ralph Mowery]

> You are obviously quite new to the wonderful world of teleprinters, and
may
> feel put off by sometimes conflicting advice on what can and can't be
done.
> I had no formal training with printers, but often not knowing what
> (officially) would not work, I did it anyway and often it did work. While
> loop voltages in excess of 100VDC are no doubt necessary for operation
over
> lines many miles long, I have found that the Teletype Model 15 works quite
> well with a loop voltage as low as 30DC. The only disadvantage may be the
> need to more carefully adjust the Rangefinder.

While you are right in that a Model 15 will work the low voltage, it really
needs to be operated with a much higher voltage (100 to 200 volts).   There
are several reasons for this.  Not counting operating over many miles of
lines, here are two of the main ones.  The simple explination is that the
higher voltage lets the magnets pull in faster.  They only have less than 20
miliseconds to be inplace if things are perfect.  The higher voltage lets
them 'snap' into place much faster.  Inductance in the coils tend to slow
down the rise time of the current.  It has to go from zero to 20 or 60 ma in
a very short time.  It has to do with the rise time or DV/DT of the circuit.
The faster this hapens the more tollorante the machine will be to outside
delays.    Another reason is the higher voltage tends to burn the oil and
stuff off the contacts of the keyboard unit.