The PP5/400 is an audio power triode, and was one of the first to give a significant output. 26 Watts of push pull audio to the loudspeakers of the time was suitable for use in a small hall. With transformers of the period being less efficient than later designs an audio power amplifier using a pair of these valves was a substantial piece of equipment, and heavy.
The box anode supported by heavy struts back to the pinch stem. The top of the anode is open as was the case for the earlier Azide process valves with the supports for the filament and control grid being held in a glass rod.
The construction matches that of the PX25 and the oxide coated filament is held in flat hooks at the ends of the tension springs.
The anode supports all run back to a collar round the pinch stem. The support for the glass rod connects directly to the pinch.
Unlike the PX25 the anode supports slant inwards to small tabs on the anode. The flat tension springs are welded to wires fixed into the glass rod.
Gettering near the base on the reverse side.
The balloon envelope has a maximum diameter of 64 mm and excluding the B4 base pins it is 138 mm tall.
References: Data-sheet & 1043. Type PP5/400 was first introduced in 1931. See also1931 adverts.
