The DM70 is a miniature tuning indicator designed for dry battery operation. The DM70 has wire leads and this valve has pins.
The DM70 introduced in 1952 was one of the first miniature devices produced by Mullard.
The display changes from minimum to maximum for a 10 Volt change on the control grid. The discharge channel is tapered and the glowing column will travel further along as the voltage is altered.
The valve came complete with this copper mounting bracket.
The thin glass tube envelope is 9 mm in diameter and, excluding the B8D base pins is 43 mm tall.
References: Data-sheet & 1040. Type DM70 was first introduced in 1952. See also1952 adverts.