The EA50 is a miniature signal diode. It was designed to be used in demodulation and other signal rectification. Mullard describe the main area of application as signal detection in television equipment. In the late 1940s television was exclusively VHF based.
The small diode section within the 11 mm glass tube.
The two wires of the insulated heater were hand threaded into the tiny cathode tube.
The thin glass tube envelope is 11 mm in diameter and, including the B3G base pins, is 47 mm long.
References: Data-sheet & 1040. Type EA50 was first introduced in 1939. See also1939 adverts.