16-mm sound motion pictures : a manual for the professional and the amateur (1953)

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268 IX. SOUND-RECORDING EQUIPMENT AND ARRANGEMENT spect to the cathodes may be accomplished with a tap from the plate supply bleeder; a positive voltage of about 50% greater than the peak voltage of the a.-c. heater voltage is usually satisfactory. In such an arrangement, the cathodes are at the most negative potential; the heaters are then positive with respect to the heaters by the amount of voltage at the bleeder tap. Manufacturers have been aware of the potential increase in demand for electron tubes of long life and of consistent performance. Such tubes have been made available on the open market only recently despite the fact that electron tubes with 50,000-hours-life performance have been common for years among the "Western Electric tubes manufactured for American Telephone and Telegraph Co. telephone repeater service. RCA has available a "red tube" series previously mentioned that is intended to be more rugged than the usual commercial tube of 1000-hour rated life; the rated life of this new series is 10,000 hours. Sylvania has recently been marketing tubes of the 1603 type with a 12-v., 150-mil heater and with an Loktal-type base. There is real need for such new tubes due to the increase in the quantity of electronic control equipment used in industry ; ordinarily, the failure of a tube in a continuous manufacturing process is a serious matter that results in losses far greater than the cost of the best tube in the market. Amplifier Component Parts. World War II taught manufacturers and their engineers a great deal about the manufacture of amplifiers and their component parts. Prior to the war, equipment was expected to perform consistently only indoors where the temperature and humidity variations were quite small. The war in the Pacific made it necessary to manufacture equipment that would perform in both the Arctic regions as well as in the tropics, since aircraft were required to fly missions in both areas and to transfer their operations from one area to another as the tactics required. Altitudes of 40,000 feet became common ; equipment was required to function in any climatic conditions and at any altitude. There were many equipment failures when the first equipment manufactured was placed in service. Transformers, coils, and condensers had to be hermetically sealed. Many materials formerly used for insulation of coils such as paper and cotton had to be eliminated in favor of non-nutrient materials such as spun glass, acetate, Vinylite, and similar synthetic sheetings and tubings. More recently, about 900 pounds of electronic equipment was installed in the warhead of a V-2 rocket that Avas fired at White Sands, New Mexico, where the equipment