With an output power of 1.5 W under a 12 V supply, this circuit makes use of transistors that are still common today. Power transistors must be mounted on heat sinks.
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,...