GB792674A - Method of and apparatus for magnetising or demagnetising magnetic record carriers - Google Patents

Abstract

792,674. Magnetic recording and reproducing apparatus. INGLESBY, J. C. VREDENBURG-. April 18, 1956 [April 18, 1955], No. 11191/55. Class 40 (2). In the art of magnetic recording, a method of magnetizing and demagnetizing a record carrier is effected by means of cathode rays. Fig. 1 illustrates apparatus in which electrical oscillations produced by an interrupter 26 and a spark coil 14 are applied to the electrodes of a cathode-ray tube 8 having an electron-pervious window, known as a Lenard window, slot-like in shape and over which a magnetic tape 2 is passed. The signal so recorded may be reproduced by an ordinary magnetic head 19, and reproduced by a loud-speaker 22 after amplification by amplifiers 20, 21, the intensity of the cathode-ray beam being adjusted by means of a valve 18 controlling the vacuum in the tube 8. The recording is comparable to that of a variable density recording in optical sound films. Such a kind of recording may be made of sound by applying a suitably modulated voltage to a control electrode 30, Fig. 2. A recording comparable to that of a variable width optical recording, Figs. 4 and 5, may be made by producing a beam having a triangular section and oscillating it over the slot-shaped Lenard windows, in accordance with the sound to be recorded, by applying the modulated voltage to the deflector plates X, X<SP>1</SP>. Fig. 7 illustrates a method by which a recording ia made in the form of transverse lines across the film by using a modulated spot beam deflected by saw-tooth voltages. Figs. 8 to 12 (Figs. 9 and 11 not shown) illustrate a method of recording very high frequencies, such as television signals, by means of a cathode-ray tube 52 having a peripheral Lenard window 49 over which the record tape 50 obliquely passes, thereby producing parallel oblique traces, Fig. 10. The modulated beam is deflected by sinusoidal X and Y voltages, displaced in phase from each other by 90 degrees, to move the beam in a circular path 47 which is then deflected by funnel-shaped deflectors Z, Z<SP>1</SP> to the Lenard window 39. Thus, if a 50 c/s voltage is applied to the X and Y plates and the diameter of the cathode-ray tube is 10 cms., a scanning velocity of 1570 cms./sec. is obtained. A scanning velocity of 2000 cms./sec. is considered sufficient for television signals, Fig. 12. Specifications 738,570, [Group XL (b)], and 788,862 are referred to.