A Style-C machine, located in the tower at Truxall, PA, that controlled three interlockings on the
Pennsylania Railroad's Conemaugh Line - Toms Run, Alum Bank, and Blairs(ville).
Originally, a version of this machine was located in Blair tower, until it was closed in 1969 and moved to Truxall.
There was also another 60" machine located in Truxall that sat next to this one:

The only thing original is the model board. The frame was from another salvaged machine, the lever plates
were made by, and I used US&S 504C code to wire up the machine, as it was the only system
I had nine full code stations of equipment for. I'm taking a guess on the lever arrangement,
based on the model board and some interlocking diagrams from the PRR/PC.

Back of the machine:

The 504C Line-Coding (LC) unit is at the top,
with the office P-4 relay mounted next to it.

Below it are two storage cabinets for the 9 stations.
These were all re-wired from some KCS cabinets.

There are Amp CPC connectors on all wiring to
the cabinets, in case they need to be removed.
Field Location for Blair Interlocking:

504C Line-Code-Storage (LCS) unit upper left, pup in the middle, and P-4 field line relay right. Stations are 234 and 235 - a PLC is mounted below.

Some shelf relays are provided to control some of the signals that I have outside.

504C was capable of 35 field locations with 7 controls and 7 indications at each station.
Codes are comprised of long and short steps (16 total), there's a chart down a little lower
with an example of one of these codes. Line is normally energized. Controls are
transmitted by breaking the line at the office - field indications shunt the line in the
field. Union would continue to use this type of line circuit in 506 and 514 code types.
Office Code Unit &
P-4 Office Line Relay
Field Code Unit &
P-4 Field Line Relay
Field Storage Unit or "Pup"

This allows another station of 7 controls and 7 indications
to share the same field code unit (pictured above).
A diagram of a single 504 (or 506A) control and indication cycle.

Click here to listen to this equipment operating
The first set of clicks (16 counts) is the office unit sending out a control request.
The second set of clicks (16 more) is the field unit reporting an indication back to the office.
504C 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.