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.
This circuit is from a Radio Electronics from April 1972. The circuit uses power transistors of...
We found this simple circuit in a 1999 documentation. It converts low-intensity sinusoidal signals (a...
This very high voltage circuit was found in the 1990 special issue of Radio Electronics...