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Lead-Sulfide Photoconductive Cells in Sound Reproducers*
BY R. W. LEE
GENERAL PRECISION LABORATORY, PLEASANTVILLE, NEW YORK
Summary — A number of experiments have been performed on the behavior of lead-sulfide photoconductive cells, as applied to sound reproduction. These include measurements of sensitivity or signal output under a wide variety of conditions in a standard 16-mm sound projector. Data have been procured with silver, silver sulfide, dye image, and iron-toned sound tracks. Measurements have also been made on the frequency response and variation of signal output with exciter-lamp color temperature.
INTRODUCTION
THE LEAD-SULPIDE photoconductive cell was introduced to the motion picture industry by Cashman1 in 1947. More recently, Anderson and Pakswer2 published a detailed comparison of the leadsulfide cell with the Si and S4 photoemissive types. A subcommittee of the SMPE Sound Committee is now studying the cell. There is evidence of widespread interest in the development, but to date the cell has not been widely accepted for motion picture sound reproduction. A report has been issued by the Motion Picture Research Council3 which concludes that "this tube shows excellent promise but indicates a need for further development."
One difficulty has been that there are not enough data at hand taken from the point of view of the equipment manufacturer to enable a real evaluation of its worth. Furthermore, not all of the data which are available (published data, advertising, and private communications from development groups) are consistent and meaningful. In addition the tube manufacturers, at least in the initial stages of development, have had considerable difficulty in obtaining uniformity of characteristics in production runs. On the other hand, there are many clear-cut advantages in the use of the lead-sulfide cell for sound reproduction. This paper will present data taken in 16-mm sound projectors which it is hoped will help to clear up some of the questions involved.
* Presented April 8, 1949, at the SMPE Convention in New York.
DECEMBER, 1949 JOURNAL OF THE SMPE VOLUME 53 691