The MHLD6 was developed for military and professional applications which demanded valves rated to operate from 6 V supplies, notably vehicle batteries.
This was at a time, later 1930s, when domestic British AC mains radios still used valves with 4 V heaters.
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 MHLD6 is also known by the pre-WWII RAF service designation of VR101.
The triode section with control grid taken to the top cap. The cathode looks to be flat across the working face.
The classic envelope is 38 mm in diameter and, excluding the IO base pins, is 95 mm tall.
References: 1043. Type MHLD6 was first introduced in 1940. See also1940 adverts.
