This peak detector has a memory to prolong the response. The circuit is from American documentation from the 1980s. The supply does not have to be symmetrical.
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,...