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Four scientists of RCA examine five of the tri-color television picture tubes developed at the company's laboratories ot Princeton, N.J., and Lancaster, Pa. They are: (left to right) E. W. Harold; Dr. E. W. Engstrom, Vice President in Chorge of RCA Laboratories Division; H. B. Law, and Dr. V. K. Zworykin, Vice President and Technical Consultant of the Division. blue — as in the RCA system, or sequential presentation of the same colors. This tube comprises a glass plate and a metal shadow mask. On the plate are 600,000 small, closely-spaced phosphor dots, each .014 inch in diameter, arranged in triangular groups. Each group consists of three dots which glow in the three primary colors, — red, green, blue — when hit by the scanning electron beam. Behind the phosphor dot plate is the shadow mask. This is a thin metal sheet perforated with 200,000 tiny holes, and acts as a mask so that each electron beam as it scans can "see" only one dot of each color group. In the neck of the picture tube are three electron guns. These generate the beams of electrons which "paint" the color pictures on the phosphor plate. The other four tri-color picture tubes described in the papers are basically similar in that the color is created by the action of electron beams on color phosphors. Tube uith One Electron Gun One of these four tubes, described by R. R. Law, of the Research Center, is similar to the three-gun produc- tion model, except for the use of one gun instead of three. This nibe and the three-gun model were shown publicly in Washington, D. C, in March, 1950. The other tubes, however, are disclosed for the first time publicly in the Proceedings. Another tube, called a "line-screen color kinescope' is described in an article by D. S. Bond. F. H. Nicoll, and D. G. Moore. In this tube, narrow parallel strips of color phosphors are used in place of dots. The single electron gun scans the phosphor strips in an unorthodox manner, the beam being deflected up and down in stairstep fashion in such a way as to scan each color in syn- chronism with the received color signal during each journey from one side of the screen to the other. An entirely different tube is described by P. K. Weimer and N. Rynn. In this, the axis of the electron gun is placed at a 45-degree angle to the phosphor screen. The scanning electron beam passes through slits in the phosphor screen and is then reflected back onto the phospiior. The emitted color is controlled by the deflection of the electron beam in the immediate vicinity of the phosphor screen. This makes the color control entirely independent of the scanning process. Grid Control Tube Still another type of tube, b.ised on principles analo- gous to the layers of emulsion in Kodachrome film, was developed by S. V. Forgue. In this tube, the layers of red, blue, and green phosphors are placed on three closely-placed screens. By controlling the voltage changes on two inters-ening grids, the color is controlled. Success- (Continued on page 31) RADIO AGE 9