Reading Company cTc equipment
Over the years, I've collected a few field locations of GRS Type-K code equipment from a few Reading Company interlockings in the area - in order to control them from the office, a homemade control panel needed to be fabricated:
Close-up of the current panels. Interlockings are (L-R) Tulp Bridge East, Tulp Bridge West, Sheps Dam, and West Laurel. There is also another small panel (not pictured) for Dock.

While the Tulp's and Sheps Dam were all on the Reading Belt Branch and controlled from the Lebanon Valley Junction Tower Machine, located along the Lebanon Valley Branch in West Reading - West Laurel was on the East Penn Branch (controlled from the Oley Tower machine, located along the Main Line just west of the Outer Station in Reading), and Dock was on the Main Line (controlled from the Schuylkill Haven machine, located in the Schuylkill Haven Passenger Station).

These are the Type-K field locations that I have in service -
The field application units are the smaller cabinets sitting on top of the larger code stepper units.

Tulp Bridge (East) is to the left - it controlled the switch and signals
on the eastern shore of the Tulpehocken bridge
(after Lebanon Valley Junction)

Below, from left to right:

Tulp Bridge (West) - controlled the western shore of the bridge
for the switch and signal from single to double track.
Sheps Dam - controlled three lock levers for CarTech and two
traffic levers for #1 and #2 tracks.
Dock - On the mainline to Pottsville, switch and signal from single
to double track.
West Laurel - End of siding unit for Laurel Siding and traffic lever
for the Low Grade.
Office Master unit and two tall application cabinets and current control panels. There is also a third tall application cabinet (to the photographers back) and a smaller control panel for Dock interlocking.

These cabinets came from "R" Tower and were wired to control Ship and Lees Cross Road interlockings when Lurgan Tower was closed.

Click to hear:
1. Office transmitting a control code
2. Office receiving an indication code
3. Office reversing a switch
(one control and two indications)

4. Field transmitting an indication code

System Organization for GRS K cTc code system.

GRS Type-K code uses long/short steps to transmit and receive control and indication codes.
The line circuit is shunt (parallel) ... controls are transmitted by breaking the line
circuit, indications are transmitted from the field by shunting the line.

With the equipment that I'm operating, 21 steps are used for a control cycle
(12 steps are for station selection and 8 for controls) and 18 steps for an
indication cycle (6 for station selection and 11 for indications).
Back end of a typical
Type-K cTc machine

The Office master unit is in the
foreground and application relay
cabinets (3) are behind.
Field stepper unit
application unit

Click here to listen
to a field location
transmit an indication