The PP3/250 was Mazda's answer to the PX4, one of the classic audio power triode valves. This probably an early version because it has the balloon shape and the electrode supports including the filament tension springs are held in a glass rod to the side of the anode. An improved version was released in 1939 the ratings given are for the improved version. The original had a maximum anode current of 40.0 mA and output power (single ended) of 2.5 Watts.
This exhibit is marked DUMMY as a production sample as is our other PP3/250. However, the filament is intact and the valve probably is a fully working valve.
The oxide coated filament is a single wire formed vertically within the anode cavity into four inverted V's.
No mistaking the sample nature of this exhibit. Note the way the electrodes are clamped to the pinch tube and held by a nut and bolt. The glass rod is secured by the vertical support.
The glass suport from the side can be seen to retain the filament tension springs.
The wide anode is ribbed to give mechanical rigidity and blackened to radiate heat efficiently.
The dome carries the Mazda identification, BVA logo and Type designation etched into the glass surface. The word 'DUMMY' was added later in paint suggesting that this example failed the specification test after production.
A closer view of the glass rod support and tension springs. It can be seen that the rod is supported at both ends as well as the middle.
The grid wire is just visible when looking up into the anode.
The balloon envelope is 57 mm in diameter and, excluding the B4 base pins, is 121 mm tall.
References: Datasheet, 1040 & 1043. Type PP3/250 was first introduced in 1932.