This exhibit is a monoscope tube for generating a television test card. The pattern is close to the Indian Head design introduced in America in 1938 but does not actually feature the Indian Head design.
The Monoscope uses a standard magnetic deflection CRT design to produce a scanning beam of electrons but in place of a fluorescent screen the faceplate connects to a metal plate inside the tube. This plate has an insulated photographic pattern engraved upon it. The scanning beam produces an output where it strikes the plate and no current where it strikes the insulation. This arrangement produces a stable image and was much more cost effective than having a camera pointed at a printed test card. It was, of course, limited to a single design. Additionally it was a monochrome only technology and its use ceased with the advent of colour television.
The Original Indian Head monoscope design.
The target pattern. Note it is fixed in place with nuts and bolts in the corners. One tube design could be used with any chosen pattern.
The neck and bulb of the tube are internally coated with colloidal graphite (Aquadag) to form the final anode.
The target again.
The front plate with central connection to the target. The central fixing is threaded.
The connection close-up.
The electron gun and base.
The target once again.
Each view should offer a different area in sharp focus.
A final view of the overall Monoscope. Thanks to Chris Gibbs G8GHH for allowing me to photograph this prize possession of his.
The end window envelope is mm in diameter, and excluding the IO base pins is mm tall.