Found in a 73 magazine for radio amateurs of the 1980s, this circuit uses a dual-gate MOSFET. This component is not currently common.
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,...