Abstract

A completely new variable-density modulator utilizing a three ribbon push-pull valve is described. The entire valve is sealed by the force of the Alnico V permanent magnet on the Permendur pole pieces. Signal is applied to the center ribbon and noise-reduction currents are applied to the outer ribbons. True class A push-pull operation is obtained from the two component single ribbon valves by the use of an inverter prism which aligns the modulating and noise-reduction edges of each aperture. — An anamorphote condenser lens is used to eliminate lamp filament striations at the valve ribbon plane. An anamorphote objective lens gives a 4:1 reduction of the valve aperture in the vertical plane at the film and a 2:1 reduction along the length of the sound track. A meter is supplied to measure exposure as well as setting up “bias.” A photocell monitor is supplied and a “blooping” light for indicating synchronous start marks. — Mathematical analysis of the exposure produced by the modulating ribbon is appended as well as a similar analysis of the four ribbon push-pull valve which the new valve supersedes.

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