The PM2B is a double triode audio output valve, this was designed to offer reasonable volume at minimum consumption from dry cell HT batteries by being operated as a Class B push-pull stage. Pure Class B suffers from cross-over distortion as the initial conduction region of the valves operating slope is non linear.
The input voltage is quoted as 40 Volts peak to peak into a 4,000 Ohm impedance. The anode load is given as 14,000 Ohms. To drive the PM2B more power was required than could be supplied from the PM1HL and a suitable valve for use as driver was the PM2DX.
The two separate triode sections with mica top supports.
The identification is feintly etched into the dome. The grid wires are wound close together.
The filament springs are above the mica. Both filaments are intact and consist of single strands.
The close wound grid is easier to see in this image.
The balloon envelope is 46 mm in diameter, and excluding the B7 base pins, is 95 mm tall.
References: Datasheet & 1043. Type PM2B was first introduced in 1933.