[GreenKeys] ring signal

[Jim Haynes]

In my very limited experience:

A small-town manual office started out with a motor-generator set, using
a six-pole motor so the shaft speed was 1200 RPM and a generator that
was not much different from the one in a hand-cranked telephone, only
a little bigger.  For operation when the AC power failed they had a
vibrating-reed interrupter that ran off the 24V office battery.  All
that was later replaced by a Sub-Cycle, which was the trade name for
a device that used nonlinear magnetics to derive 20 Hz from the
60 Hz power.  There was a self-contained motor-generator for battery
backup to those devices.  And the switchboard had an old magneto
crank telephone for use in an emergency.

When this was replaced by a larger dial office there were two motor-
generator sets.  I believe one was powered by AC and the other by
the 48V battery; and these had the additional circuits to generate
dial tone and interrupters for busy tone and that sort of thing.



jhhaynes at earthlink dot net