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|Featured CED Patent No. 3,842,194|
The 1971 system had a density of 1000 grooves/inch and a disc rotation rate of 360 RPM. The marketed system had 9541 grooves/inch and rotated at 450 RPM.
This patent describes a three layer disc consisting of a vinyl substrate (10) coated with a thin layer of conductive aluminum (11) followed by a thin dielectric layer of polystyrene (12). The final system used conductive vinyl (doped with minute carbon black particles) for the entire disc.
The stylus (20) shown above was made of sapphire, and had a tantalum electrode (23) embedded inside. The marketed system used a diamond stylus, and the electrode material was titanium sputtered directly on the trailing edge of the diamond stylus rather than being embedded. A later illustration in this patent shows that RCA was also experimenting with the direct sputtering of tantalum on the trailing edge of the stylus in 1971.
This patent mentions electron beam mastering as the preferred method. Electromechanical mastering was used in the final product and is mentioned as an alternative method in this patent.
The disc player described in the patent is a top load design similar to audio turntables of the period in which the operator places an uncovered disc on the turntable by hand.
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