US&S 506 cTc Timecode Control System

Union Switch & Signal had several types of 506 cTc code: 506, 506A, 506B, and 506C.
All used a shunt line circuit, which wired all the field locations in parallel with
the office, so if the line wire broke - only stations after the break would drop offline.

506 and 506A were capable of 35 field locations with 7 controls and 7 indications at each
station, using 16 steps (1 conditioning, 7 station selects, 7 functions, and 1 delivery step.)

506B was similar to 506A except it used plug-in type relays.

506C was capable of 35 field locations with 7 controls and 35 indications at each station.

All 506 systems used KP Magnetic Stick relays for control registration.
Because KP's are used, 506 uses "progressive" delivery of controls.
This means the control is delivered to the KP relay the instant it is transmitted during the coding steps
Office Code Unit
Field Code Unit &
Line/Starting Relays
Field Storage Unit &
Field Pyramid Unit

(Added more stations
to a single field coder)
KP Final Stick Relays

Used in the field to
register control codes
The rear of a large machine
showing the office storage units,
which store the indications from
the field locations.
506A Test Set

This is used to test
office and field
units to make sure
they are functioning

All station, control,
and indication cycles
can be tested, along
with voltage and
timing tests.