The HD22 is a battery double diode triode for receiver use. Marconi alone produced an HD21 that only differed from the HD22 in that it operated with a bias point of -1.5 Volts.
The two valve sections are the same size and built in the same way.
The anodes in semi-profile.
This is the triode section with the grid connected to the top cap. The central spring tensions the single hairpin filament.
Here is the double diode section. The filament can be seen through the mica. One anode is the outer shell and the other is formed by the vertical rods that match the size and spacing of the triode grid supports thus making efficient use of the production tooling.
The paper ring holds in place the wire that connected to the external metalising paint. Fragments of the paint can be seen on the glass.
The classic envelope is 45 mm in diameter, and excluding the B5 base pins is 97 mm tall.
References: Data-sheet, 1040 & 1043. Type HD22 was first introduced in 1934.