Cinematographic annual : 1930 (1930)

Record Details:

Title:
Cinematographic annual : 1930
Date:
1930
Publisher:
Hollywood : The American Society of Cinematographers, Inc.
Volume:
Cinematographic annual : 1930
Leaf #:
000408
Language:
English
Subjects:
Motion Pictures, Motion Picture Technology
Collection:
Books
Format:
Books
Contributor:
Media History Digital Library
Sponsor:
{"Media History Digital Library","Richard Koszarski","Jeff Joseph"}
Coordinator:
Media History Digital Library
Description:
Date Added:
March 21, 2024
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388 • MXKMATOGRAPHIC ANNUAL The photoelectric cell circuit is shown in Fig. 6. In a high impedance circuit such as this, local interference, sometimes termed static, is readily picked up and if not guarded against will produce serious distortion in reproduction. PHOTOELECTRIC CELL CONDENSER 2 MEGOHMS 10 MEGOHMS VACUUM TUBE I POLARIZING BATTERY FIGURE 6 Since the energy level is so small, induced current may be appreciable in comparison to the sound currents themselves. In addition, there are other electrical effects which may create some distortion. Because of the low level of this power, it would be dangerous to transmit it any great distance before it has been amplified. Therefore, an amplifier (called a PEC amplifier) is placed immediately adjacent to the photoelectric cell circuit to amplify the power to a level at which it can be safely transmitted. This amplifier increases the photoelectric cell output approximately 50 decibels or a power ratio of 100,000 to 1. The photoelectric cell and amplifier are encased in a heavy metal box which is fastened to the frame of the projector and the frame is carefully grounded. Further precautions are taken to insure against mechanical shock by carefully suspending the tubes of the amplifiers. The output of this amplifier is approximately the same as that of the magnetic reproducer used in disc reproduction. This will permit the remainder of the reproducing system to be