The sensor is S1 in this alarm that we found in a Radio Electronics magazine from May 1971. Several sensors can be used in series. The SCR supports equivalents from the 106 series.
This simple circuit with SCR and unijunction transistor appeared in Radio Electronics magazine in July...
Found in a 70s RCA manual, this circuit uses a transistor of the time for an UHF L band...
Found in American documentation, this circuit from the 90s uses components from that time. The...