This only markings on this exhibit are the figures 96 and 6D2. The 6D2 is a miniature double diode and this is not. A close visual inspection against other tuning indicators shows a positive match for the TV4.
The TV4 is a 1936 tuning indicator, it has the then standard British 4.0 Volt heater.
The TV4 was the first Mullard magic eye on the UK market. It was more compact than other available types (which made it popular with set designers) but early specimens had short lives. This was corrected by alterations to the internal design including adding a helical grid like electrode round the display cathode. This can be seen in the TV4A but not this exhibit..
Typical construction with the amplifier triode below the display section.
As expected the triode has a small front-to-back dimension.
A closer view showing the spot welds of the anode to the supports. The anode connects to the display control electrode.
The display bowl. The display cathode does not have the addition of a protective grid.
The end window envelope is 26 mm in diameter, and excluding the Ct8 base pins is 72 mm tall.
References: Data-sheet & 1043. Type TV4 was first introduced in 1936. See also1936 adverts.
