This circuit makes use of a mechanical delay line to produce the reverberation effect. This is a '80s setup, showing both channels for a stereo system.
This is an old test circuit for integrated TTL counters, feeding a Nixie tube, common at the time....
This traditional crystal radio circuit, but which has a modern version with diode, was found in an...
This headphone amplifier using a pickup coil can be used as an extension for devices such as TVs,...