The Hivac XY is an audio output pentode designed for hearing aid amplifiers. The design is advanced for UK production in the mid 1930's with glass foot construction.
The Hivac identification. At the top are the filament tension springs.
The grid wires can just be seen through the mesh anode. The suppressor grid is the easiest to see.
A closer look at the top mica components. The filament springs are made in one piece.
The SM5 base. The larger pins are the filament connections. The pin connections from Thrower would suggest a different starting point.
The underside of the base.
The thin glass tube envelope is 18 mm in diameter, and excluding the SM5 base pins is 62 mm tall.
Reference: 1043. Type XY was first introduced in 1935. See also1935 adverts.