This variable frequency circuit was found in a Popular Electronics from the 90s. The circuit outputs to a small speaker and can be powered by voltages as low as 3 V.
We found this variable regulator circuit in a Radio Electronics issue from July 1984. It is one of...
The MC4741 consists of a quadruple 741. The power supply must be symmetrical, and the resistors must be...
Suggested by Sprague in the 1980s documentation, this circuit can control three-phase AC motors....