This circuit is from a 1965 General Electric manual. It uses components from the time that admit equivalents. The SCR can be the TIC106 and the LDR of any type.
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...