GB390157A - Improvements in or relating to photographic sound recording apparatus - Google Patents

Abstract

390,157. Variable resistances. ELECTRICAL RESEARCH PRODUCTS, Inc., 195, Broadway, New York, U.S.A.-(Assignees of Silent, H. C.; 6182, Glen Oak, Hollywood, California, U.S.A.) Sept. 28, 1931, No. 26983. Convention date, June 19. [Class 37.] Comprises optical sound-recording apparatus wherein the recording current is passed through a transmission device such as an amplifier the gain of which is substantially constant for all values of the current below a predetermined value and is decreased when the current exceeds that value so that excessive variation of exposure of the photographic emulsion is prevented. In the arrangement shown by Fig. 2, the outputs from transformers 50, 51 are each supplied to the grid of a valve such as 55 through a control device comprising two potentiometers one of which is composed of two resistors 52, 53 in series while the other 54 is bridged across the resistor 53. A wiper arm 60 of the potentiometer 54 may be moved to increase the input to the valve 55 from zero to the total voltage across the resistor 53. Further movement of the arm 60 is adapted to open a switch 56 and move a switch 57 from a contact 58 to a contact 59 so that the input may be increased gradually up to the maximum voltage developed across the secondary of the transformer 50. The amplified output from the transformer 50 is supplied to the ribbons 12 of the light valve 14, while the amplified output from the transformer 51 is rectified and applied to the control circuit of the valve to produce a " dynamic biasing current." Specification 362,915, [Group XL], is referred to.