GB782572A - Improvements in and relating to reproduction from magnetic records - Google Patents

Abstract

782,572. Magnetic record-reproducing apparatus. BRITISH BROADCASTING CORPORATION. May 18, 1955 [June 1, 1954], No. 16250/54. Class 40 (2). [Also in Group XXXIX] A magnetic record-reproducing apparatus comprises a reproducing head having a magnetic core 10 with a gap 11 over which the record 15 is passed, a winding 12 surrounding part of the core and a conductor 13 to which is applied current generated by an oscillator 14 the current being of frequency f greater than half the highest frequency to be reproduced; this current generates in said part of the core a flux which has no linkage with the winding 12 and saturates or at least substantially reduces the permeability of the said part of the core so that there is generated in the winding 12 an oscillation of frequency 2 f amplitude modulated by the intensity of the remanent flux in that part of the record 15 which is disposed at the poles of the head, and a demodulator 18 is provided to extract the modulation from the modulated signal. The oscillator 14 which may contain a frequency doubler or divider applies an oscillation of frequency 2f to the demodlilator, and connected between the winding 12 and the demodulator is a band-pass amplifier ,17 having a centre frequency of about 2f. The output signal may be amplified by an amplifier 19. Unbalance caused by unidirectional extraneous field or by residual magnetization in the core may be counteracted by selection of the polarity and adjustment of the value respectively of a voltage source such as a battery 20 and a variable resistor 21 connected across the winding 12, or by the provision of a permanent magnet, not shown, whose position relative to the head is adjustable. As shown, the core 10 is of high permeability low electrical conductivity material such as powdered magnetic material with a suitable binder and the conductor 13 is bare, but in various modifications, not shown, the said part of the core is of reduced cross-section, the conductor is a strip clamped between two halves of the core, the conductor has an insulating covering in which case the core need not be of low electrical conductivity material, and the core yoke has a large gap bridged by a wire or rod of electricallyconducting magnetic material constituting the conductor 13.