[GreenKeys] Re: Fw: Teletypewriters, part 2

[Jack]

Jim et al,

Ma Bell used the SOTUS selector for routing messages to the
central office frame, repair bureau, business office and installation
shops to pass around service orders. The SOTUS selector had
some Model 15 similarities, but was even heavier duty. In the
roughly 8-9 years I worked on TTY for Ma Bell, I don't recall
ever having to fix a SOTUS selector. They just kept on going,
and going, and going...eventually these networks were
replaced with the "COMDAT" video terminal and then
the Model 40's.

In most of the Telco's business officess there were two
seven-foot rack cabinets which housed the SOTUS selector,
control relays and the loop rectifiers. The routes could be
detected by the selector or the operator at the Model 19 table
could manually select a route with a "turret" full of lever
switches and switchboard-type lamps.

The distant TTY's, mostly 15 RO's, operated over a single copper
pair to ground. One side of the pair controlled the TTY's motor/alarm
and the other side was an "inverse neutral" signal line. An open
line was a mark and  negative battery was a space. In some cases,
we had a hard time getting the 20 loop current through the pairs, so we
would actually use two shorted pairs. Since there were "company
service" lines, the company didn't do a good job of record keeping
on the circuit assignments. So, if a line went bad, we would usually
have to rebuld it (re-engineer) because we had no idea where the
pairs went. In many cases tha pairs would actually go through different
CO's!

Another quirk of this system was that there was a line feed index
on the RO's that would only let the machine turn off when the paper
was aligned correctly (vertically). The paper was about 6 inches wide and
was sprocket feed. The turret operator would send manual line feeds if the
station light didin't go off at the end of a a message. When the light went
out,
the paper was at the right spot. Most of us hired in the early 70's
had never seen anything like this system (of course, yours truly was only
a Ham who knew how to fix a TTY...I never saw ANY types of
systems previously).

The most amazing system was the 83B3...(was it the 81D that had
the BLANK-PAUSE-SPACE feature?).

Jack WA2HWJ
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