This simple circuit for headphones or small speakers was found in documentation from the 90s. The circuit works with voltages from 5 to 9 V and has good gain.
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,...