What do you want to know? Used on 1A2 systems. I've got a frequency generator around here some where. Got it from a Nortel Modular system that it had been attached to to supply ringing to an external 90 v ringer.
I found it in a residential apartment building and wasn't sure what it would have been used for. It was unplugged from the wall but still attached to a ca/pr - was too lazy to trace it but I assume for a/the enter-phone...maybe?
Could have been, I suppose. Ask one of your OLD business installers, or ask a buddy to borrow a business Installation manual from way back when...actually I should have one around here as well. When I get home today, I'll look up the details.