Patent GB-344524-A (GB)
Title: Improvements in or relating to light valves particularly for use in recording sound
IPC: G11B7/00
Filed: 1929-12-09
Abstract: 344,524. Light valves for recording sound &c. ELECTRICAL RESEARCH PRODUCTS, Inc., 195, Broadway, New York, U.S.A.-(Assignees of Gent, E. W. ; 251, Speedwell Avenue, Morristown, and Potts, L. M. ; Oak Street, Tanafly, both in New Jersey, U.S.A.) Dec. 9, 1929, No. 37774. Convention date, Jan. 31. [Class 40 (ii).] Relates to devices for varying the amount of light transmitted from a source in response to electric current variations, of the kind in which a pair of conductors adapted to carry the varying currents are arranged at right-angles to a magnetic field so as to define a slot through which the light passes, the width of the slot being varied by relative movement of the conductors. According to the invention, the device comprises a casing containing the windings and one of the polepieces of the field magnet, a cover for the casing carrying the other polepiece, the vibratory conductors, and the necessary adjusting and tensioning devices. As shown in Fig. 3, one polepiece 5 is screwed to a casing 1 which contains the field winding 7. The other polepiece 6 is mounted on a detachable cover 2 which can be secured to the casing by means of a screw ring 3, the cover being held in a definite position by projections, not shown. The polepieces are accurately spaced apart, when the parts are assembled, by providing studs 13, 14 on the cover which bear against flanged portions of the polepiece 5. The vibratory conductor which defines the light-slot consists of a filament 18, Fig. 4, stretched across the gap between the polepieces, which are bored to form aligned passages. Light enters the valve at 44, passes through the slot formed by the filament, and enters a lens tube mounted in a recess 43, the passages 44, 45 being threaded, and coated with black paint to render them non-reflecting. The filament 18 is secured at one end to a take-up screw 19, passed round a pulley 20, and attached at the other end to a screw 21, the parallel strands lying in a small channel in the polepiece 6. Conductors 22, 23 leading to external terminals 16, 17 on the casing enable sound-modulated current to be supplied to the filament. A preliminary tensioning of the filament is effected by means of the screws 19, 21. The proper positioning of the strands of the filament relatively to each other and to the polepieces is determined by providing two pairs of bearing members or " pincers " 30 which engage the wire as shown and are finely adjustable by means of differential screw devices 28, 31, 32 shown in Fig. 7. These adjusting devices are mounted in insulating blocks 26 secured to the cover 2. Strips 34 of ivory adjacent to the members 30 form bearing surfaces for the filament. A final adjustment of the tension of the filament is effected when the cover is in position by varying the position of the pulley 20. For this purpose, the pulley is mounted on a bowed spring 40 carried by a bracket 35 which is pivoted at 36 under the control of a spring. A cone 41 on a threaded rod passing through the cover bears against the member 35, so that by adjusting the cone the position of the bracket 35, and thereby the tension of the filament, can be varied.