Found in a 1965 General Electric circuit manual, this circuit uses SCRs from that time. Modern equivalents according to the power can be used.
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,...