[GreenKeys] AP Model 15 information

[Dan Beach]

What a pleasure to see the activity on Green Keys!  I'm a new list member
with some experience back in the early '60s: I built a terminal unit from
scratch, rebuilt an old Model 15 machine (from a pile of parts!) and
ultimately had the fun of seeing TTY messages from Navy ships. Later, I had
two Model 33ASR which we used as terminals for our now primitive DEC PDP-8
and Altair computers.

I have recently acquired a Model 15 which was used by the Associated Press.
It appears to have a straight 120vac power connection (although the plug is
the 3-pin  connector in Y-layout, usually associated with DC), along with a
red/green pair which went to the phone line connection. In addition, there
is a panel in the rear of the machine I've never seen before which has a
transformer, capacitor and various  diodes and ic's.  Does anyone know if I
am safe assuming that this is the loop power supply? And if so, what would
have been the signal provided thru the phone line to trigger the relays?
Just polarity reversal?

I have a manual on the way, I'm told, but I'd sure appreciate any advice
from folks who have dealt with the old AP machines before. And I figured I'd
ask a few questions before I applied power.

Thanks.
Dan Beach/KD4WLI