We found this circuit in a Popular Electronics of the 90s. The circuit can be easily mounted today, as the components are common. The SCR can be the TIC106.
In this interesting circuit from Popular Electronics, the output voltage is the square root of the...
We found this circuit in a documentation from the 90s. It lets frequencies around 1 kHz pass,...
This is one of many configurations with a 4-input mixer transistor that can be found on this...