Motion Picture News (Oct-Dec 1929)

December 7, 1920 Motion Picture News 53 Double Channel Amplifier Systems and Servicing for Sound Installations Factors for Consideration in Determining Need for Reserve Equipment — Apparatus Checking Devices angle. Therein lies our interest. is imperative and the past problems of the radio industry are the present problems of the talkie field. Of course, several exceptions are present. Acoustics as found in theatre installations were never approached in radio. The average radio receiver installation does not involve as many units in addition to the amplifier proper, as a talkie system. But notwithstanding, the amplifier problems are the same in both. Hum, distortion, poor quality of reproduction, lack of operation and other such difficulties are attributable to identical defects. Perhaps the magnitude of a radio installation does not approach a talkie system, but the ailments of the midget and the giant are the same in character— if not in scope. Checking Operation The paramount consideration in radio service has been measurement of operating potentials, such as filament, grid and plate voltages and plate current. Not only do these observations furnish an indication of the conditions of the sources of potential and the actual operating potentials, but the measurement serves as a circuit continuity test, which when interpreted is the most rapid method of arriving at the existing trouble. Some of the public address systems installed in theatres are already equipped with the required indicating instruments, but thousands of installations must be serviced in a hit or miss way. A great deal of talkie equipment is very similar to that employed in radio installations. With perhaps two exceptions, although one (R.C.A.) is not wholly so, vacuum tubes employed in talkie systems are the identical tubes employed in radio. The sole exception without qualification is Western Electric, who employ tubes of their own manufacture. Since the other tubes are of the type employed in conventional radio installations, they are employed in identical manner under like conditions. Testing-Sets Speed Service Consequently, testing devices developed for radio work are wholly applicable for the testing of talkie amplifiers. One such unit has proved a tremendous boon to the radio service business. Adaptation of similar apparatus to the uses of the theatre sound installation may offer the means that in the future will facilitate checking and servicing talkie systems. This unit is known as the set analyser and consists of an arrangement of meters, switches and inserts, whereby ampli (Continued from page 35) Service fiers can be tested under load. The inserts provided with the set analyzer enable connection to the tube socket and measurement of operating voltages and tube currents without interruption of service or disarrangement of the wiring or the apparatus. The meters employed in the testing device obviate the need for equip ment upon the amplifier panel, because it is possible to determine grid bias voltage filament voltage, plate voltage and plate current by simply removing a tube at a time from the amplifier, inserting the tube into the correct tester socket and inserting the correct tester insert into the vacant amplifier tube socket. After that it is a mere matter of turning a switch or two to secure the desired operating potential and current values. Such equipment is of vital importance to the service man called upon to work with unmetered amplifiers and is likewise of tremendous, value to the operator who is responsible for the perfect performance of an unmetered or not completely metered system. Let's Face the Facts, Folks — Modern theatre requirements are no longer ordinary from points of manufacture and sales, but a case for real Engineering. V alien Policy: Every transaction must be of Mutual Profit. Achievement knows no "Dead-Line." Manufacture in accordance with Changing Demand. Quality and Service Unchallenged! E. J. Vallen Concentrated application to one special line, over a period of fifteen years, enables us to promptly meet standard and special stage conditions with V alien FourWay Mask for Large Screen Vallen Track and Baskets for Moving Sound Horns