12-9] 



SPECIAL DISPLAY DEVICES 



663 



together. The transfer characteristic of each gun must be altered to 

 compensate for the different efficiencies of the three phosphors. If equal 

 radiant energy is not obtained from each color, then the mixed hue is 

 predominantly tinted by one color. 



The difficulties associated with the fabrication of a uniform shadow mask 

 and phosphor dot plate are being resolved by using mass production on 

 photoengraving and silk screen techniques. Even with these mass produc- 

 tion techniques, the stringent alignment and uniformity requirements make 

 these tubes complex to manufacture and therefore expensive. Continuous 

 operational misalignment and sensitivity to external magnetic fields make 

 this tube unsatisfactory for military display. For the home television 

 system an external magnetic shield of high permeability is used to minimize 

 the effects of external fields. In a moving vehicle such as an aircraft, 

 vibrations are enough to vary the convergence of the beams even with a 

 tube shield. 



The Chromatron. A simpler color tube which has been flown in experimen- 

 tal systems has been given the trade name of Chromatron. This tube has 

 the advantage of displaying multiple colors with a single beam and the 

 further advantage of not being sensitive to magnetic fields. Although it is 

 not as simple to assimilate into compatible home television systems as the 

 shadow mask tube and is therefore not in general use for this purpose, it 

 will certainly become a useful radar display tool when persistent color 

 phosphors are developed and when the grid vibration problem is solved. 

 The Chromatron tube, as shown in Fig. 12-41 a, uses a single beam which is 

 magnetically deflected over a phosphor screen. The three primary-color 

 phosphors are arranged alternating in horizontal strips across the screen 

 and the electron beam made to focus at any point on any one of the color 



Deflection Yoke 



Color Grids- 



Phosphor Screen^ 



Fig. 12-41a The Chromatron Tube. IJ. Gow and R. Dorr, Proc. IRE (Jan 1954) 



p. 309] 



