The MHLD6 was developed in 1940 for military and professional applications which demanded valves rated to operate from 6 V supplies, ie vehicle batteries, it is directly equivalent to the CV1101. The MHLD6 is also known by the pre-CV register RAF service designation of VR101.
The double diode triode was used in superhet radio receivers. The diodes would rectify both signal and AGC lines, and the triode would act as the first audio amplifier stage.
The front carries the M-OV lozenge etched into the glass with the Type designation within. On this side the printed lettering includes VR101 and the old stores code of 10E/280. The circle with MWT within looks to be a reference to Marconi. Not visible is the crown amd AM initials for the Air Ministry.
The top mica showing the heater and the grid connection to the top cap.
The classic envelope is 39 mm in diameter and, excluding the IO base pins, is 105 mm tall.
References: 1043. Type MHLD6 was first introduced in 1940.