This alarm circuit was found in April 1975 Radio Electronics magazine. The circuit uses a 12 V power supply and relay but can be modified to work with other voltages.
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...