[samm_cz]

Interesting, in ex. USSR and Czechoslovakia i am aware only about "2 wire" systems, but i heard also about "IBM" one with a 3 wires, so now i know what it was for, thanks :) Here master clock was producing 1m or 30s duration impulses. I also heard about "hybrid" systems where both digital timestamp and 1m impulse were delivered, so clock was able to choose what to use. What is funny that there were no common standard. 6V, 12V, 24 and 60 - all were common! So few times i saw converters from one to another. One of the last "master clock" devices from Pragotron was based on IC circuits, but principle was the same - https://aukro.cz/matecni-hodiny-pragotron-eh40-6960978702

[jcrawfordor]

I've heard of hybrid digital/analog systems in the US, I think a few smaller companies introduced them as an upgrade path - IBM/Simplex/Standard pretty much dropped support for these clock systems totally but lots of institutions already had them installed, so a cottage industry popped up of companies that made compatible equipment to keep them working and upgrade them over time. As far as I know virtually everything in the US was 24vdc but I'm sure there's some odd exceptions out there.

I've always had a weird interest in these systems since they tend to pop in large old buildings and are one of the many odd building systems you have to figure out sometimes - along with vacuum controlled HVAC and old phone systems. A small side project of mine right now is trying to get a working dental office communicator light system.