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 thin glass tube envelope is 10 mm in diameter and, excluding the B3G base pins, is 35 mm long.
References: Datasheet & 1040. Type EA50 was first introduced in 1939.