Exhibitors Herald and Moving Picture World (Apr-Jun 1930)

EXHIBITORS HERALD-WORLD May 3, 1930 30 SOUND PICTURES BLUEBOOK SCHOOL . . . SHOWMANSHIP By F. H. RICHARDSON BLUEBOOK SCHOOL QUESTION NO. 49. — What kind of warning does an amplifying tube filament give before it finally fails? What should he done as soon as this warning sign appears? What is likely to happen in event the projectionist does not heed the warning? Are noisy amplifying tubes found occasionally and what is the cause of the noise? ANSWER TO BLUEBOOK QUESTION NO. 40 7 he question z tias: Describe an amplifying tube. Tell us what potential each of its three elements carries. By what is the grid charged ? By what is the filament charged and what is the effect of heating it? THERE were a great many answers to this one and still they are coming in. To date the following have answered acceptably : Karl Friedrich, G. L. Doe, John Doe and Bill Doe, Chicago ; Gayle Grubaugh, Bernard A. Omlar, Dan Johnson, William Nally, Abe Myers, Rudolph Roller, G. L. Ridder, Amel Dikersen, Arthur Quick, Frank L. Peterson, John Cotty, D. G. Henderson, M. L. Matteson, Fred Mallaby, T. L. Moreland, John Wilson, F. D. Raind, Henry Little, T. D. Dubois, Andy Cadley, R. Riderhouse, T. R. Mally, T. D. Alexander, G. T. Beatty, Fred T. Smith, Leo G. Sands, Bob Jones, T. Singer, P. D. Campon, John Furman, Harry Diener, Harry L. Hudson, T. D. Mason, Elmer Phillips, Fred Emery, Philip Allbright, F. T. Moore, Thomas T. Oberdorfer, Alex B. Lee, H. T. Baker, Mack Miller, G. L. Ridder, Charles Herson, J. C. Richards, Frank M. Eberle, R. Campbell; Jake Hendershot and Bert McBride. Of those answering correctly, there were two who did exceptionally well; namely, Karl Friedrich and Arthur Quick. Neither of these answers are long, so we will print both. Quick says : “An amplifying tube is a bulb of thin glass of somewhat varying height, fixed in a metal base in which suitable means are provided for connecting it quickly but effectively to an elec tric circuit. In this bulb, or tube, are three elements, one of which is a filament coated with a certain compound which will throw off minute particles of negatively charged electricity called electrons when it and the filament are heated. This filament is heated by a flow of current coming from a storage battery, with which it is connected in series. “Another element is a rectangle of perfectly flat metal, which is also charged by a current from a storage battery, so that when the tube is in operation, a current flows between it and the filament, across the space separating it from the plate. The electrons supply the conducting element. “The third element is the grid, in which no current flows but which is negatively charged by the photoelectric cell circuit. This charge varies in proportion to the current induced by the light action upon the photoelectric cell, or by the disc pickup if a disc is the source of sound. The amount of bias this grid has, of course, varies in proportion to the sound. It opposes the flow of current from filament to cell in exact proportion to the amount of bias present from one instant of time to another. The filament carries a negative, and the plate a positive, charge.” Friedrich treats the matter thus (it is evident he keeps up to date) : “In answering question No. 40 I would say that an amplifying tube consists essentially of a base* with suitable prongs and provision for mounting same in a suitable socket. On this base is attached the bulb, or tube, made of glass, somewhat after the manner of an elec tric lamp, and like the lamp, different tubes vary widely in size and shape. Inside of the bulb is a filament and a plate spaced some distance apart. Between the plate and filament a grid is placed. None of these elements touch each other, nor are they connected to each other except through external apparatus. The interior of the tube is evacuated ; that is, the air is removed and then sealed. That about describes the ordinary three-element tube. Lately there have come on market tubes with more than three elements, the extra elements usually being more grids. For instance, we now have available the screen grid tube, which has an extra grid surrounding the plate, and the pentode, which is like the screen grid tube and in addition has a third grid surrounding the original, or control grid. I. have even heard some rumors of a tube with seven grids, but so far have failed to locate an accurate description of it. “The filament of an ordinary three-element tube is supplied with what is called the ‘A’ voltage, which is a comparatively small voltage with a heavy current draw. The purpose of this voltage is to heat the filament and force electrons from it. The plate is supplied with a large positive potential, the purpose of which is to attract the electrons boiled out of the filament. The grid is charged with a negative potential and also with the signal voltage, which serves to control the flow of electrons from filament to plate. For this reason in multi-grid tubes, this grid is called the control grid.” LACK OF SHOWMANSHIP FROM a city in the middle west comes a letter signed by the four projectionists comprising the projection staff of a fairly large, excellent motion picture theatre. It reads most interestingly : “Dear Brother Richardson : I, who will sign this letter first, have been appointed a committee of one by the projection staff of this theatre. We ask your advice. If you publish the matter do not name either the theatre or city, as aside from what we shall complain of, our manager is a really fine boss and a good fellow. Here is our trouble: “We have a very nice theatre. It seats 1,800. The auditorium is beautifully decorated and the acoustics are very good, though much work had to be done on the walls and ceilings after sound was installed before that was true. There is an excellent orchestra, well uniformed ushers and good ventilation. In fact, our management seems very willing to spend money for anything which will improve the what-the-audiencessee effect, but there it stops short. “Here in the projection room we are held to the most rigid economy. We must use projector parts until they just won’t work any more. We cannot seem to convince the manager that an exciting lamp is not still quite all right, merely because its globe is blackened inside, or its filament, is in the shape of a more or less correct letter S. ‘It gives just as much light as it ever did,’ he will say, and nothing we can do will alter his opinion. And so it is with all other things. Now, Brother Richardson, whatever quarrels we may have had with you in the past, we all believe that everyone in the business does respect you and is willing to listen to what you say with respect; also, what you say seems usually to have a lot of effect. W'e do not think our manager reads your department very much, but he knows of your work and I know from talking with him that he has considerable respect for it. _ Will you not therefore print an article telling the reasons why he is wrong in his attitude? We believe it will really help us a lot if you will, and that it will help others, too. May we thank you in advance for your kindness in this matter, and for the almost inestimable help we have all had from your books and your department?” First of all, gentlemen, I object to you saying this is mv department. It is NOT. It is OUR department. You pull that again and I’ll slap you on your wrist darned hard!!! Certainly, I will accede to your request, because it is right and proper that I do so as far as I am able. .. From what you have said, it is plain that your manager means no wrong. He really believes he is working economically for his employer. He doubtless is a very busy man and has dismissed projection with the thought ( Continued, on page 40, colunwi 3)