This circuit was found in documentation from the 1980s. The integrated circuit is from the time and the voltage depends on the desired power, and the component's datasheet should be consulted.
This is a commercial radio circuit from the 1960s. The circuit was found in a Japanese publication from...
The integrated circuit used in this 80's differential amplifier is a quadruple version of the 741...
This touch or proximity sensor circuit was found in a Popular Electronics from 1992. In the...