GB471359A - Improvements in means for and methods of forming mosaic electrodes for use in electric discharge tubes - Google Patents

Abstract

471,359. Cathode-ray tubes. FARNSWORTH TELEVISION, Inc. March 2, 1936, No. 6255. Convention date, March 13, 1935. [Class 39 (i)] A mosaic photo - electric cathode is formed by providing a roughened insulating surface on to which silver is deposited from a point source, a caesium coating being applied after the silver has been oxidized. To provide the roughened surface a mica plate may be scored or powdered quartz is blown in suspension' on to a mica plate 1, Fig. 1, provided with a " side mask so that only the centre square 2 has the quartz surface; the plate is now mounted on a metal backing 4, in an envelope 11, Fig. 1, containing a chamber 14 with a small orifice and with a deposit 17 of silver. A surrounding coil 19 is used to vaporize the silver after the envelope has been evacuated, and a discharge may be caused to take place between the chamber 14 and plate 1 to direct the vaporized silver in substantially straight lines on to the plate. The smooth part of the plate receives a uniform silver deposit ; the quartz particles, owing to their uneven form, receive the silver deposit 17, Fig. 4, on the outer parts only, shading the deposit adjacent the mica foundation and thereby forming discrete islands of silver deposit. When the plate is sufficiently coated, the envelope is broken along the line 20 and the end with the coated plate 1 is used to form part of a discharge tube 21 ; the discharge tube has a pipe 26 in connection with an exhausting tube 25, and a caesium supply 27. After exhaustion, oxygen is admitted to oxidize the silver deposit, this taking place in the presence of a glow discharge obtained by a coil 19; the caesium is then vaporized into the tube 21, the connection 10 to the smooth silver deposit on the outer edge of the plate 1 being used to test sensitivity of the photo-electric surface during processing, the surface being illuminated for this purpose.