[GreenKeys] Selector Magnet Driver WECO

[Jack]

ZCZC

I spent a relaxing day (!) tracing the wiring and connections for
a Western Electric J70161A-1 L1 Selector Magnet Driver assembly.
This unit mounts in a Model 28 Electrical Service Unit (LESU)
and was designed as a replacement for the WECO 255A polar
relay module. This thing can be identified by looking for
a rounded-corner 315A polar relay (looks a little like the
314 type of mercury relay) and a small transformer on a standard
LESU plate. My unit has a 1969 date code.

The module interfaces to a 20 or 60 ma. teletype loop and
provides selectable internal bias current for the polar relay
as well as a keyed 60 ma. HV loop for the connected TTY. Two
terminal screws allow for shorting out the polar relay contacts,
thus "blinding" the TTY to incoming traffic. This is often used
with auxiliary reperforators, etc.

The resistors, diodes and filter capacitor are mounted on
an insulating board and wired with standoffs. Two of the
current-limiting power resistors (approx. 10 watts?) get pretty hot
and the insulating board on my unit is nicely charred
from the heat. However, when I set it up on the bench, it worked
fine.

If anyone needs info for one of these modules, I can send you a copy
of the schematic (it was drawn with VISIO, but I can send
it as a WORD document).


Jack K0TTY

NNNN