Man, everyone is out to beat me up! OK, I was referring to the card itself being quiet without having any mechanical relays. Yes, John, all WECO 1A2 and Comkey systems used mechanical interrupters. Their 6B "Dialog" advanced intercom system was sort of a PBX/intercom system hybrid that offered solid state ringing and lamp flash, but it was short-lived. Tone Commander's ML-8000 beat it up price-wise, so I doubt that the 6B lasted more than five years.

I know for sure that ITT's 601 had a solid-state interrupter and that was the only option. I bought enough of them to know. These cards had a very high failure rate due to heat issues.

The San/Bar one fit into a dedicated slot on their own 15-line panel and wasn't interchangeable with other systems, but it was definitely solid state. I am pretty sure that Plant Equipment made a solid state interrupter as well for their panels, but I never worked with them.

Ed Vaughn, MBSWWYPBX