The magic eye class of tuning indicator originated in the US and Type 6E5 was one of the earliest types. Almost all European types are more-or-less directly copied from it.
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 helix of a small space charge grid.
The amplifier triode below the display.
Here the helical space-charge grid around the cathode can be seen.
Face view of the end window with the centre cover to hide the electrodes.
A closer view.
The UX6 base pins. The wording on the base is 'Licensed only to extent indicated on carton'.
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 6E5 was first introduced in 1935. See also1935 adverts.
