GB242821A - Improvements in and relating to methods of and apparatus for the production of phonographic and the like records - Google Patents

Abstract

242,821. British Thomson-Houston Co., Ltd., (General Electric Co.). Jan. 7, 1925. Optical apparatus; electric and magnetic soundboxes; dampers. - In making sound records by electromagnetically operating a cutter, the current variations which cause the vibrations correspond to variations in light which are in accordance with and produced by the sound being recorded. Fig. 4 shows the general arrangement and the electrical circuit employed. The sound affects a transmitter 41, the diaphragm of which vibrates a mirror 45, which reflects light on to a photoelectric cell 43. This cell is connected in known manner in the grid circuit of a thermionic valve 44, the plate circuit of which includes a source of current 51, a resistance 52, condensers 53, 54, and coils 32 wound in series on opposed magnets 20, 21. Between the poles of the magnets, on which the coils are so wound that a current variation which strengthens the poles of one magnet weakens those of the other, a strip of magnetic material 14 carrying a cutting jewel 18 is mounted. The magnet poles are close to the cutter, and symmetrically arranged relatively thereto. The recording device is shown in detail in Fig. 1, which is a plan seen from underneath. The permanent magnets 20, 21 are adjustably clamped on a plate 10, having a projecting lug 11 on which is pivoted a frame 12 by which the vibratory strip 14 bearing the cutter 18 is carried. The strip extends across the frame 12, within which damping material 17 such as fibre or rubber is arranged on either side of the strip. The magnet poles 31 carrying the coils 32 extend into the centre of the frame 12, which can be adjusted about its pivot by a screw (not shown). The assemblage including the cutter is adapted to be moved along guide 60 so as to traverse the rotating blank on which the cutter operates. Specification 199,741 is referred to.