The TZ40 is a magnificent audio triode that was designed for high power use. In class B a pair would deliver 175 Watts at 5% distortion. The TZ40 was the successor to the T40.
The signal input would be 220 Volts peak to peak between the two grids. The anode load would be 7,000 Ohms. Maximum anode dissipation is 40 Watts.
It is quite possible that the main use for this device would have been modulators for small AM transmitters.
The maker's name Hytron and Made in USA.
The base cap carries the old stores code of 110E/37 and the Crown and AM showing that this valve was made for the UK Air Ministry.
The valve was supplied in a plain carton with basic lettering on one side. The date looks to be 1942.
The balloon envelope is 51 mm in diameter and, excluding the UX4 base pins, is 149 mm tall.
