Double diode triode

A double diode triode is a type of electronic vacuum tube once widely used in radio receivers. The tube has a triode for amplification, along with two diodes, one typically for use as a detector and the other as a rectifier for Automatic gain control, in one envelope. In practice the two diodes usually share a common cathode. Multiple tube sections in one envelope minimized the number of tubes required in a radio or other apparatus.