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.
This exhibit has Mazda etched in the dome of the envelope.
The anode is supported by a cage clamped to the pinch stem. The top electrodes are held in place by embedding the free ends in a glass rod. This method of construction was superseded by mica sheets that fitted tightly into the the shoulder of a shaped glass bulb.
The top glass rod has angled supports fitted that are then spot welded to the tension springs for the filament.
The dome carries the Mazda name and at the top is the Type designation - only partly visible.
The tension springs and a small strip of mica.
The two zeros of the PP5/400 are just visible in this picture.
The balloon envelope has a maximum diameter of 63 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.
