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This exhibit is a three inch electro-statically deflected CRT probably from the late 1930s or early 1940s. This came complete with a small mu-metal shield and probably the paper label that was originally wrapped round the tube neck had to be removed to accommodate the shield.
The electrodes are secured to ceramic tubes that have wires running centrally through them. The Y deflection plates have no flare and this is unusual. The X deflection plates do have a flare to them.
The electrodes are held to the glass neck by metal fingers. The connections pass through a glass foot base rather than a pinch. So it is possible that this is a post-war replacement.
The flare on the X deflection plates is plainly seen as is the cylindrical focus anode.
The ceramic tubes can be seen to be hollow with wire running through. This method of construction gives rigid supports plus insulation for the high voltage lines.
Another view of the X plates.
The domed screen.
The B12B base pins with locating key on the central spigot.
The mu-metal shield just slides over the plastic base and is 70 mm long. The inner lining is black felt. In position the shield is firmly held in place. The lettering on the shield refers to the CV138 - the post war EF91.
The end window envelope is 41 mm in diameter, and excluding the B12B base pins is 177 mm tall.
Reference: Observation.


Updated March 26, 2019.
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