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 was obtained in a 1990 documentation and can be powered by the previous circuit...
This RF amplifier step has a dynamic range of 140 dB and can amplify signals from 0.5 to 40 MHz....
This oscillator with different outputs has frequencies selected by the S2 switch in 3 bands. We...