There was an earlier version known as 1A1, and apparently a 1A, 2A, and 2B before that.
The 1A1 units that I have seen, were built as a complete unit, where the 1A2 systems were modular, using plug in cards for the various features. I have no information on 1A, 2A, or 2B systems.
The phones could be wired up without a KSU, and would operate as a regular phone, without lights, or hold. The ringers in the phones were wired to a dedicated pair, and could be strapped to any line, or to multiple lines via a diode matrix.
The basic KSU had a power supply for the lamps, and a line card for each line, which handled the hold function, lamp control, and ring indication. The basis line card was a type 400. Lamp voltage was normally 10vac.
The wink-on-hold feature required an interruptor, which plugged in to the KSU, and provided the pulsed lamp voltage for lines on hold. This was normally powereed by the 10vac lamp supply, although other voltages were available.
I worked at a radio station where all the lamps, and interuptors were powered by 24vdc from a bank of batteries, which also supplied all the control circuitry within the studios. The PBX (Western Electric 711B step-by-step dial PBX) was powered by another bank of batteries at -48vdc.
KSU without interruptor.
KSU with interruptor.
KSU with a type 401 manual intercom card in place of a line card. Signaling was handled by using either a spare button on the phone, or add-on button(s) wired to extra pairs, and a add-on buzzer powered from the lamp voltage supply. The buttons in the phone could be changed from latching to momentary by removing a screw.
There were several types of dial intercoms, depending on the number of stations desired. The smaller ones could be cards in the KSU, or a seperate unit.
You could wire the phones to do many different things. We used to use the buttons on the phones to provide contact closures to other (non-phone) devices, and the same for the lamps.
This would have been a Call Director in a PBX type environment, with a busy lamp field.
The basic Call Director was simply a 1A2 type phone, with additional buttons/lamps. The earlier ones simply added additional 6 button strips, and the later ones were 10 button strips. Earlier call directors were commonly 18 or 30 buttons, and later 10, 20, and 30 buttons. There were also some custom monster phones.
There were some wiring differences between the 6 button strips, and the 10 button strips.
Normally each line used 3 pairs of wire, 2 for the phone line, 2 for the button (A1/A), 2 for the lamp (L/LG).
For a 6 button phone/5 line phone, this would be 15 pairs, plus one for the ringer, leaving 9 spare pairs for add-on devices such as buzzers, speakerphones, etc, using a 25 pair cable. Some phones were equipped with 15 or 18 pair cables instead.
For 10 lines, this would require 30 pairs, not including any pairs for ringer, or add-on buzzers, etc, but by bussing all the A1 leads together, the spare A1 leads for lines 2-5 could be reused as A leads for lines 6-9. The same trick was used with the LG leads, thus reducing the number of pairs needed to 19 (plus one for the ringer), leaving 5 spare pairs for add-ons in a 25 pair cable. Additional 25 pair groups were added for additonal 10 button rows.
The phones with more buttons sound like late version Call Directors.
I found a collectors website, with a listing of many many types of Western Electric phones, including many that most people have never seen or heard of.
-- I am Me, I am only Me, And no one else is Me, What could be simpler? --