The magic eye class of tuning indicator originated in the US and Type 6E5 was one of the earliest types. Here it also carries the American government procurement code of VT-215. Almost all European types are more-or-less directly copied from the 6E5 design.
Early specimens, such as 6E5, had short lives due to 'burning' of the fluorescent target and poisoning of the cathode coating in the centre of the target area. This was later cured by enclosing the display part of the cathode within the spiral of a small space charge grid.
The display changes from open to closed for a 7.5 Volt change on the grid.
The makers name and Type on the base but the 6E5 is also etched onto the glass.
The triode amplifier is mounted below the display on a common cathode.
A frontal view of the pinch and electrodes.
The space-charge grid is wound with two different diameters and has no connection. However, it appears to touch the cathode tube outside the display bowl.
The display window.
The end window envelope is 29 mm in diameter and, excluding the UX6 base pins, is 87 mm tall.
References: Data-sheet, 3002 & 1043. Type VT-215 was first introduced in 1935.