This circuit uses a dual-gate MOSFET, a rare component today. We found it in American documentation from the 1980s. The rest of the components are 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,...