Machlett made this valve for the UK Government. The box construction is substantial and heavy. The sandwich construction has two layers of stiff board with corrugated card at the centre. Two corrugated card inner sections with cloth cross pieces hold the ends of the valve. A label on the lid shows that it was accepted at SNSO Hazlemere December 1943. Much later it was sold as a collector's item for £15 as a brand new VT-31. The box is 290 mm square and 585 mm tall.
