This sound intensity meter was found in a 90s Elektor. The circuit uses an integrated device from the time that is not common today. The indicator is a milliammeter.
This is the traditional unijunction transistor relaxation oscillator circuit for the audio band. The...
This is half of a 4-channel amplifier from a system published in the October 1971 issue of Radio...
This circuit works both as a grid-dip (transistorized) and as an oscillator. The circuit is from a...