The DH77 amplifier triode with twin signal diodes on a common cathode. It was designed for use in superhet receivers at the end of the IF chain and as the first audio amplifier feeding the output stage.
The paper Marconi label.
The Diode anodes can be seen as a pair of vertical plates. See6AT6 for internal details.
The thin glass tube envelope is 17 mm in diameter and, excluding the B7G base pins, is 46 mm tall.
References: Datasheet, 3002 & 1040. Type DH77 was first introduced in 1950.