We found this circuit in the September 1971 Radio Electronics magazine. The SCR can be any of the 106 series and the buzzer can be replaced by a relay according to the supply voltage.
This simple radio was found in a Popular Electronics from the 90s. L1 and L2 have 100 turns on a...
This circuit was found in Radio Electronics magazine from the 90's. The circuit is for small NiCad...
This automotive circuit was obtained from an 80's schematic from the integrated circuit factory...