GB322729A - Improved method of photographically recording acoustic frequency oscillations - Google Patents

Abstract

322,729. Gramophone Co., Ltd., Browne, C. O., and Tedham, W. F. July, 31, 1928. Metallic-vapour apparatus.-Acoustic frequency oscillations are recorded photographically by impressing the oscillations upon an electric glowdischarge device so as to control the light emitted from the positive column of said discharge device, the latter having a filling of mercury vapour at a pressure between 0.5 cm. and 1 cm. of mercury and substantially no other gas or vapour. One form of discharge tube 1, Fig. 1, suitable for direct insertion into the anode circuit of a valve amplifier is made of quartz or is provided with a quartz window and has mercury electrodes 2 and heating coils 3; platinum electrodes may be used. In a modification, Fig. 3, aT-shaped quartz tube has mercury electrodes 2 between which an ionizing discharge is produced by a direct-current source 8, a stabilizing resistance 13 being inserted as shown. The acoustic current source, such as the secondary winding of the output transformer 9 of an amplifier, is connected to a solid electrode 7, and to one of the terminals of the source 8 to a, point on a resistance shunting the source 8, or to a second solid electrode inserted in the horizontal part of the tube 1. A polarizing discharge is established between the electrode 7 and one or both of the mercury electrodes by means of a direct-current source 11 having a resistance 12 in circuit. Only the light from the acoustic current glow in the vertical portion of the tube is used, means being provided to prevent the light coming from the ionizing discharge between the mercury electrodes from affecting the photographic film. The heating coils 3 keep the tube at its correct temperature which is stated to be about 175‹ C.