Motion Picture Herald (Jul-Aug 1936)

July 2 5, 19 3 6 MOTION PICTURE HERALD 85 Hill::" TECHNOLOGICAL The BLUEBOOK School By F. H. RICHARDSON [To join the Bluebook School merely send in answers. Place name and question number upon first sheet. Address F. H. Richardson, No. 3 Tudor Lane, Scarsdale, N. Y.] BLUEBOOK SCHOOL QUESTION NO. 33.— (A) What is good maintenance practice with respect to stocking spare sound equipment parts? (B) Give us your views regarding lens ports. This is an important matter so do not be too sparing of words and ideas. Answer to Question No. 28 Bluebook School Question No. 28 was: {A) How is amplification secured in a three-element tube? (B) Name the essential things served by projection room ventilation. The following made acceptable answers : C. Rau and S. Evans ; D. Danielson ; G. E. Doe; B. Devietti ; J. R. Prater; A. L. Cooper; D. Pollock ; W. Limmroth ; F. Bochert ; H. Edwards ; C. Champney ; P. and L. Felt ; W. C. Brown; C. A. Ellison; H. B. Smith; C. Lonie ; C. L. Loft ; W. H. Edmonds ; C. G. Jones; M. and J. Devoy; C. and S. E. Gay; J. F. Seidman, G. L. Snow, R. Galley and R. T. Digby; C. L. Hauber and R. B. McCullough; G. D. Jones; M. J. O'Brien; C. Hawkens; S. Myers and O. L. Harris ; E. N. Quinn, H. T. Bell, N. Nathan and S. D. Singer; L. A. Keller; T. H. Morton, L. and F. H. Klar _; F. K. Monroe ; F. H. and L. Savior ; J. Lansing and R. D. Oberleigh; H. K. Abernathy and R. Tomkins ; N. R. Tomlinson ; H. F. Stacy and C. Stuart ; J. Jacobs ; J. S. Knight and F. T. Hamilton; B. L. Shaw; W. D. Samuels; H. T. Todd and L. A. Dodson ; D. Emmerson ; T. B. Danielson ; R. L. Norton ; C. C. Lowery, M. Hicks and J. L. Durante ; D. J. Green, J. W. Ruther and M. L. Lawrence ; O. R. Johnson ; R. E. Hartmann ; R. Morris ; C. J. McCabe and R. Holmes ; R. Mills and J. R. Perkins ; V. Burton ; I. C. Croft ; W. Burns and T. R. Fanning ; H. and F. C. Winkle ; L. T. Hunt ; G. Johnson and L. R. Spooner; H. V. Nathan; H. H. Lantry; E. B. Hibbard ; J. E. Smith; G. W. Scott; P. Larcher and L. W. Morgan; H. D. Lally ; T. N. Powell and N. T. Brown ; W. D. Wagner and E. C. Moore ; J. Farraro ; R. Hubbell ; M. Wentworth ; L. B. Hardy ; D. D. Orr; P. Redman and N. G. Kilgen ; A. Garlock and J. B. Roth ; M. R. Ray ; H. E. Lytle ; 0. E. Parker and L. L. Lewis. [Note : The "diplomas" will be issued at the completion of one full course in the Bluebook School. You may start at any time, but must send in answers every week unless you can supply a reasonable excuse. — F. H. R.] Section (A) is answered by B. L. Shaw as follows : 'What we call 'amplification' is not really that at all, but in reality the controlling of a strong current by a very much weaker one. The three-element tube has three electrically active elements, called respectively the 'plate,' 'grid' and 'filament,' all located in a vacuum established within a glass enclosure or 'tube.' The action is as follows : "The filament is connected to two wholly different circuits, one of which supplies d. c. current for the purpose of raising its tempera ture to incandescence, in which condition it throws off or emits clouds of negatrons energized by each of the two before mentioned circuits. Those having their source in the heating current, which we will call current A, return to the filament, since electrical action is always within its own power source and the circuits connected therewith. "A second circuit, which we will call B, has its negative side attached to the filament, its positive side being connected to the 'plate,' a sheet of thin metal, though for the purpose of greater coolness some manufacturers use a metal ring for a plate. In any case the plate must present considerable area to the negatron action I shall describe. "Thus we have filament and plate terminals of a circuit separated by space in the vacuum tube. When in action the incandescent filament fills the vacuum with negatively charged particles of electricity called 'negatrons.' This is termed a 'space charge.' Disregarding the filament circuit heating current negatrons, those that have their power source in current B, being electrically charged, would of course be attracted to the plate and thus a current would be established in circuit B that would be of even voltage and strength and of power equal to the ability of its power course to overcome the resistance set up in the circuit, including the vacuum space itself. "However, between the positively charged plate and the filament that is negatively charged in so far as has to do with circuit B is a 'grid' that is connected with the negative side of the F. H. Richardson's BLUEBOOK of PROJECTION • New sixth edition. Projection, sound reproduction and trouble-shooting all In one handy volume. Also features quick-finding index system for instant reference. Order to-day. $5.25 Postpaid QUIGLEY BOOKSHOP ROCKEFELLER CENTER NEW YORK very weak photo-electric cell, hence is negatively charged. Now, as we all know, positive attracts negative, whereas negative repels negative. Since to reach the plate the negatrons from current B, which form the B current through the vacuum space, must pass through the grid, it follows that more or less of them will get through against the grid negative repulsion force, according to the instant-to-instant power impressed upon the grid by the P. E. cell circuit. That action should be easily understood. When the negative repulsion power (grid voltage) is less, more negatrons get through to the plate ; when it is greater, less negatrons can pass. "Remembering that at each instant of time the P. C. cell voice current alters in exact proportion to the amount of light reaching its active element from the film sound track, it is evident that the B current will be modified by the condition described exactly in accordance with the voltage variations in the voice or P. E. cell current. In other words, the stronger B current voltage will be made into an exact duplicate of the weaker voice or P. E. cell current voltage." [Note: I submitted the foregoing to two of our best sound engineers, who both agreed that while perhaps not exactly correct from the scientific vSewpoint, it nevertheless contains nothing basically wrong. Personally I regard it as the most understandable explanation of amplification I have yet seen — understandable to the non-technical man, I mean. — F. H. R.] J. R. Prater explains it this way : "In a three-element vacuum tube, amplification is secured through its valve-like action that enables a weak current to control a much stronger one. The three essential elements of the tube are anode, cathode and grid. More complicated tubes have other elements added, but they merely serve to modify or assist the three essential ones. "The positive wire from a high voltage (moderately high only. — F. R. H.) pure d. c. power source is connected to the anode (Plate. — F. H. R.) and the negative wire to the cathode (filament. — F. H. R.). This, together with its power source and wires, forms the plate circuit. "When the cathode is heated (brought to incandescence.— F. H. R.), negatrons are emitted from it, a great number of which are attracted to the positively charged anode, or plate. This flow of negatrons forms the plate current (through the tube vacuum space. — F. H. R.) and under this condition the current flow would {Continued on following page)