A local restaurant that was built in the '70s still has its original Simplex system with two 4050/4051’s on 4050-80 light plates (w/o “fire” lettering). There are also three 4251-30 break glass pull stations and several System Sensor heat detectors.
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Like I said, it seems I’ve seen 4251-30 break-glass pulls used a LOT on 1970s Simplex systems with 4051+4050-80s, like one of my old schools. But I’ve also seen several 1980s Simplex systems that use 2903 horn/visual alarms and break-glass 4251-30s as well (especially in schools.) And I have seen a fair amount of systems from both eras that just use single-action 4251-20 pulls (and in one case, a school that used to have an old Edwards system from 1957 that was upgraded during a 1973 addition to a Simplex 4208 system, keeping the original Edwards pulls in the original 1957 structure!)