The QP22B is a battery double pentode, designed for quiescent push pull class B audio amplification. Class B amplification produces considerable distortion at the points in the cycle where the valves move from cut-off to conduction. The advantage is that when not driven by a signal the power consumption from the HT battery is low.
The total power output is 1 Watt and was aimed at driving a loudspeaker, quite a luxury when battery powered.
The valve can be operated with automatic bias obtained from a resistor in the common HT negative lead. Such a resistor should be bypassed at signal frequencies by a 50 µF capacitor. For minimal distortion the total anode current (both anodes) should not fall below 3 mA and the screen grid supply should be 120 Volts.
The side view shows the pair of matching valves within the envelope.
The top view showing the filament support and tensioning coil springs and the grids inside the anode. The springs have hooks passing down through the centre of the coil.
The classic envelope is 39 mm in diameter and, excluding the B7 base pins, is 89 mm tall.
References: 1043. Type QP22B was first introduced in 1938. See also1938 adverts.
