The DH30 is a double diode triode for use in superhet receivers where the diodes provide signal demodulation and AGC voltage and the triode acts as the first AF amplifier stage.
The heater is designed for use on mains powered sets or 12 volt vehicle batteries.
The control grid extends either end of the mesh anode. The cathode tube is rectangular. The screening box above the lower mica shields the two diode anodes.
The B7 base pins.
Thanks to Mark Mallison for sending the image.
The balloon envelope is 50 mm in diameter, and excluding the B7 base pins is 125 mm tall.
References: Data-sheet & 1043. Type DH30 was first introduced in 1934. See also1934 adverts.