[GreenKeys] Loop Supplies

[Jim Haynes]

Another standard of the old days was the Stancor something or other that
provided an adequate voltage for a loop supply plus a 6.3V heater voltage
that could be used for a low voltage DC supply for RS-232 circuits and
the like.

Something I've used recently is a transformer from Mouser with 120/240V
primaries, and used only one primary on 120V and used the other as a
secondary for the loop supply, and there was a low voltage for low
voltage supplies.  Figure I'm not loading it anywhere near the rated
load so it's OK to use only one of the primaries.