General Electric Light Valve for the Talaria video projector

General Electric Light Valve for the Talaria video projector
Tube modulateur de lumière pour vidéoprojecteur
Lichtventil für Videoprojektor

This is certainly the weirdest vacuum tube in my collection: it contains an electric motor, a spinning disc, and oil!

Shortly after World War II, GE Electronics Department General Manager, Dr. Baker bought the rights to a Swiss developed projection television system called Talaria. The Talaria approach made use of a rotating optically-flat glass disc with a thin film of oil squeegeed over a deposited transparent conductive coating. This film was then raster-scanned in a vacuum by an electron beam which was modulated by a video signal as in a standard television picture tube. The electric field in the oil film between the deposited electrons and the conductive coating result in a decreased oil film thickness, the effect being more pronounced where a greater number of electrons were deposited. By mounting this disc in a Schlieren optical system and shining a light from a Xenon arc lamp through the scanned image on the oil film, the thickness variation on the oil film was converted into a variation of light intensity so as to project a bright television image on a screen. The properties of the oil used were adjusted so its image decayed in the time between television frames in the same manner as the luminescent decay of a picture tube phosphor.

The Talaria principle was developed by a General Electric commercial business into a successful line of television projectors for theater or other large screen use.

Video on YouTube: GE Talaria projector light valve