Museum of the Broadcast Television Camera

Marconi MkVIII Television Camera viewfinder picture

Marconi MkVIII Television Camera viewfinder picture

Spotty tube troubles

This viewfinder tube is OK but problems with the tubes are not uncommon, many viewfinder tubes made at that time had the "spotty problem".

The tube face plate is made in two parts, the tube face proper, with phosphors and a vacuum on the inside, and a flat front plate. A sort of safety glass. In between the two is a gel? filler which was meant to have good optical transmission characteristics. In the problem tubes some sort of growth possibly bacterial has set up home in the space between the sheets. Or it may just be a generic defect in the manufacture allowing air in and the deterioration following on.

Many cameras from this period have this problem with their viewfinders, Marconi MkVIII's seem to be heavily affected but the newer MkIX's and Philips cameras less so.