Oh, yes. I remember it well. My father's real estate office had one of these systems. 50 pair per station.

The KSU was the size (and weight) of five cinder blocks an the lamp flash wasn't done by a motorized interrupter. It was a card that consisted of a bunch of timed relays. It was noisy, certainly not something that could be installed in any quiet environments. All cards had a simple metal ring to pull them, like you would see on a keychain. We laugh now, but it was pretty high-tech in 1976.

It's funny, the receptionist used to amaze me how she could tell when a call was getting ready to come in, even before the phone would begin ringing. It was because the amplifier/speaker that provided the warble tone ringing was "asleep" until a call arrived. She could hear the click of the speaker when the KSU sent power to the amplifier in the set. Too much info...........

This was one of the first times I ever saw two-pair 1A2 (T/R/A/L) and was likely the motivational factor in Western Electric and Bell coming out with the Comkey systems. At least Comkey systems kept the amplifier board in the sets hot all the time so there wasn't the click.

Ed Vaughn, MBSWWYPBX