Found in an old Popular Electronics this circuit is still current. The SCR can be of the 106 series and the relay according to the voltage used in the supply. The voltage can be 12 V.
This traditional configuration that any Series 139 comparator can use is found in the 1990...
The circuit shown in the figure can be used to detect vibrations or to provide amplified acoustic...
This toy organ was found in Popular Electronics from January 1967. It can be constructed from...