The PM22A is a battery audio output valve for use in domestic broadcast receivers. It was made during the early 1930s: introduced in 1931 with the B4 + side terminal base and later, in 1936, on a B5 base.
The power output is low at 350 mW and so efficient loudspeakers were required to achieve an adequate listening volume. The output is lower than the PM22 but the filament power consumption was also less.
For correct operation the anode load should be 19,000 ohms.
The classic envelope is 38 mm in diameter, and excluding the B5 base pins, is 94 mm tall.
References: Data-sheet & 1043. Type PM22A was first introduced in 1931. See also 1931 adverts.