An acquaintance came to see me, all self important and gloating - he had a Baird Televisor lamp and it was picked up for a fraction of it's true value, obtained for a song and Stukey Bill had sat in front of it for ages, yeah, right.    Well done said I with a brittle smile and a demeanor tinged with a soupcon of envy, however, this soon evaporated just like his dreams of a healthy profit when he produced his prize with a flourish and I lampooned his hopes by showing him a photo from contemporary Mullard documentation showing a similar specimen of his 'Televisor lamp' : -  

Pretty good huh, but alas not Televisor material.   What my hapless pal had stumbled upon was a photocell designed for sound-on-film projectors, although there were no markings I pronounced it a Mullard emission photocell type 20CV - unfortunately, slightly less desirable than a Televisor lamp!!!

These devices crop up from time to time and the technology behind the is interesting and not often described so, in  my next blog entry, I shall describe the theory, operation and usage of these valves and indeed other photo-electric phenomena - I'll bet you can hardly wait!!!!