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| Keywords: Airplane Detection Appt002.jpg Three-stage amplifying set device for detecting airplanes Acoustic Laboratory Frankford Arsenal open Operation top 1 Connect condenser detector to input ; 2 Connect telephone to output ; 3 Decrease grid leaks to minimum resistance ; 4 Set filament controls at OFF position ; 5 Turn on A Battery by pulling out snap switch ; 6 Increase filament current of last tube to almost full value ; 7 Set filament control knobs of other tubes to index marks Never turn past these marks ; 8 Increase grid leak resistance until maximum amplification is obtained ; 9 No further attention is required National Institute of Standards and Technology 1926-08-06 National Institute of Standards and Technology The images in the Airplane Detection Apparatus Photographic Collection are in the public domain and are not subject to copyright in the United States However please pay special attention to the individual works to make sure there are no copyright restrictions indicated Individual works may require securing other permissions from the original copyright holder Use of the images from NIST Digital Collections is not restricted but a statement of attribution is required Please use the following attribution statement National Institute of Standards and Technology Digital Collections Gaithersburg MD 20899 PD-USGov National Bureau of Standards National Institute of Standards and Technology Sound locators Frankford Arsenal | ||||
