This receiver was found in a 1924 book by Gernsback. The circuit uses three tubes and is powered by 3 batteries of different voltages, common at the time.
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,...