The PM2A is a low power battery audio output valve and the output power is quoted as between 0.15 to 0.27 Watts. The load resistance required was 8,000 Ohms. This equates to high impedance headphones or a high impedance horn loudspeaker. The filament would be run from a 2.0 Volt accumulator.
The basic details of the valve are etched into the dome of the envelope.
The balloon envelope is 44 mm in diameter and, excluding the B4 base pins, is 85 mm tall.
References: 1931 data-sheet & 1043. Type PM2A was first introduced in 1930. See also 1930 adverts.