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.![](../pics/aaq0159a.jpg)
The two separate triode sections with mica top supports.![](../pics/aaq0159b.jpg)
The identification is faintly etched into the dome. The grid wires are wound close together.![](../pics/aaq0159c.jpg)
The filament springs are above the mica. Both filaments are intact and consist of single strands.![](../pics/aaq0159d.jpg)
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: Data-sheet & 1043. Type PM2B was first introduced in 1933. See also 1933 adverts. |