Here is a Standard Electric Time model 000-015 intercom telephone set, with an inspection date of April 14, 1976, shown in various states of assembly.
This unit was originally part of a school intercom system. All phones in the system were connected together in parallel with the power supply, which rectified and filtered the output of the same transformer that supplied 24vac to the clock system (schematic of power supply). When any phone was taken off-hook, a Sonalert buzzer sounded to notify office staff. Each room in the building had a buzzer connected to the bellboard for general signaling, so the manual signal buttons on the bellboard were also used to call rooms.
The design of the handset is nearly identical to a Western Electric G3 type. The tube on the handset cord has “COMM SPECS 1974” printed down the side, so I suspect that is the name of the company that actually manufactured the parts. Upon initial testing, I found the original transmitter and receiver to have oddly weak performance, so I replaced them with real WE elements (comparison shown above; original parts on top, WE on bottom). The WE parts were drop-in replacements. Note also that the receiver, transmitter, and hookswitch were simply wired in series, to make the most basic type of functional telephone set.
So, I want to use it as a normal telephone set. It is shown above with the wiring non-destructively modified to connect to a Western Electric 685A subset. This connection requires five conductors—three to connect the handset components to the 425 network and two to allow the hookswitch to interrupt the line. I used some type of multi-pair cable I had lying around for the test and pictures, but I could (and likely will in the future) use a piece of ethernet cable to connect these units. Including the WE receiver and transmitter, this set now operates and sounds exactly like a normal 500-type set. Now if only I had somewhere to put it… (More may be added to this page in the future.)