The DH63 is a double diode triode and was designed for receiver audio use.
The diodes would be for signal and AGC rectification and the triode would act as AGC amplifier or first audio amplifier.
The Marconi paper label on this M-OV valve.
The Triode is at the top with the diodes below a central mica. The bright box is the screen and the diode anodes are the two rods either side of the common cathode.
The classic envelope is 38 mm in diameter and, excluding the IO base pins, is 97 mm tall.
References: Data-sheet, 1040 & 1043. Type DH63 was first introduced in 1937. See also1937 adverts.