RAF Valve Receiving VR55 has the commercial equivalent of the EBC33, a double diode triode with a common cathode. The design dates from the late 1930s (1937-1940).
Typically double diode triode valves would be used in superhet receivers at the end of the IF amplification chain. One diode would produce the AGC voltage and the other would be used as the AM signal demodulator feeding into the triode as a first audio amplifier.
The zinc paint has flaked off at the top and this has revealed the triode section. The lead from the control grip is connected to the top cap.
Below the triode bottom mica and on the same cathode tube are the small plates that form the diode anodes.
The classic envelope is 30 mm in diameter and, excluding the IO base pins, is 86 mm tall.
References: Data-sheet, 1040 & 1043. Type VR55 was first introduced in 1938.