This exhibit is sealed in a polythene pouch and was supplied to the UK Air Force. The pouch is sealed as a CV1074 and contains an American 6J7G indicating equivalence. The CV specification shows that the KTZ63 was the prototype.
Type 6J7 design is a contemporary of the Magic Three and almost as ubiquitous. Although originally designed as a detector its linear characteristic and good internal shielding 6Q7G made it a natural choice for audio.
It was for two decades the international standard valve for audio amplifier input stages and audio systems generally. The Mullard-Philips type EF37A, for many years the standard British low-noise audio pentode, is really a 6J7G under another name.
The base cap carries the crown and AM logo of the UK air ministry. Affectionately known as Arthur Mitchell to war time service personnel.
Here the valve and its CV label can be seen. Valvo was a valve distributor.
The manufacturers details and stores code.
The classic envelope is 39 mm in diameter and, excluding the IO base pins, is 98 mm tall.
References: Private communication & datasheet. Type CV1074 was first introduced in 1936.