International projectionist (Nov-Dec 1933)

28 INTERNATIONAL PROJECTIONIST December 1933 (Left) FIG. 1 — P.E. characteristics of potassium-hydride caesium-oxygen-silver cells and (Beloiv) FIG. 2 — Effects on the photoelectric sensitivity of various thicknesses of the outer layer of caesium I 70 z o 60 ^u 50 n P < 40 X 5 O w 0. I £8 5° . NORMAL N^'SURFACE 4.5 ATOM_A LAYERS \ \o.3 ATOM \ LAYER 4000 5000 6000 7000 8000 9000 10,000 11,000 12,000 WAVE-LENGTH IN ANGSTROM UNITS 7000 8000 9000 10,000 11,000 WAVE-LENGTH IN ANGSTROM UNITS 12,000 previously used. The relative response of the two types of cathodes to tungsten light of color temperature 2710° K over the spectral range from 3,000 to 11,000 Angstrom units is given in Figure 1. To obtain a highly sensitive cathode surface, and one whose long wave-length limit extends so far into the infra-red, it is very essential that the residuum of caesium in excess of that necessary to combine with the silver oxide be held within extremely close limits. Studies have been made of the effect of additional amounts of caesium on the photosensitivity of the surface. In these studies the spectral response of a normally prepared surface has been obtained, and then additional caesium allowed to condense on the cathode surface at such a slow rate that the change in sensitivity of the surface with added caesium coverage could be observed. Effect of Added Caesium Typical results of this kind are shown in Figure 2. From this figure it can be seen that the long wave-length limit recedes from about 12,000 A. to 9,600 A. by the addition of about 0.3 layer of caesium. When 4.5 layers have been added to the surface, the long wavelength limit has receded further to 8,400 A. The integrated area under each curve is proportional to the total sensitivity for that surface condition. For 0.3 of an atom layer added, the total High efficiency and a plate always cool — two more of the 6 advantages of the new DUO VAC 205-D tube. Install a set today. — Adv. sensitivity is reduced to 60% of its initial value, and for 4.5 layers it is further reduced to 25% of its initial value. The 3A type photoelectric cell has been standardized for sound picture applications. Its cathode is of the caesium-oxygen-silver type. A still higher output is desired from this cell than the increased sensitivity of its cathode makes possible. To further increase the sensitivity, the cell is filled with argon to a pressure of a few hundredths of a millimeter of mercury. With anode potentials of less than 20 volts the behavior of the cell is identical with the high vacuum one. For anode potentials greater than 20 volts the anode current rises above that of the vacuum cell and diverges rapidly from it. At 90 volts potential the anode current is approxi Cut Your Carbon Costs by 20% with the SYNCROFILM CARBON SAVER Not a gadget but an accurately machined equipment designed and used by practical projectionists. Backed by the reputation of Weber, makers of the famous Syncrofilm sound equipment. For All Sizes of Carbons Easy to operate, with the work being done in a jiffy. No trouble, no fuss, no dirt. Get one now and cut your carbon costs by at least 20%. WEBER MACHINE CORP. 59 Rutter St. Rochester, N. Y. COMPLETE UNIT CONSISTS OF: 1 Frame for Drills 2 Drills With Handles 3 Positive Adapter Rods 12 Extra Points for Adapters 2 Negative Adapter Rods 1 Aluminum Dust Cup 1 Bushing for Drilling Negative Carbons Price $20— Complete Be sure to specify size of carbons used when ordering