The HA2 is an M-OV valve that duplicates the American 955. The acorn valves were designed to have low capacitances and therefore work to higher frequencies than the normal valves. This exhibit is branded Osram - usually the brand name for consumer valves. We also have the HA2 branded Marconi.
The 955 was introduced by RCA in 1934 and the UK made devices did not achieve the success of the American product and acorn valves were eventually black-listed for UK government equipment use.
The Osram paper label.
The electrodes appear to be mounted between ceramic disc supports rather than mica sheets.
The original box showing the Osram name, the BVA logo and a price of 45/- (45 shillings) - quite expensive. The box is constructed in the same way as the HA1 box
The thin glass tube envelope is 13 mm in diameter, and including the base pins is 32 mm tall.
References: Datasheet. Type HA2 was first introduced in 1936.