This circuit doubles the frequency of a rectangular signal applied to its input. The circuit has a 30 kHz input to obtain 60 kHz signals. We found it in a 1964 Electronic Design.
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,...