GB692446A - Improvements in or relating to gramophone pick-ups and recording heads - Google Patents

Abstract

692,446. Gramophone pick-ups and recorders. THERMIONIC PRODUCTS, Ltd. Jan. 3, 1952 [Oct. 6, 1950], No. 24499/50. Class 40 (iv). A pick-up or recording head is arranged to take either a top or bottom suspension stylus. A top-mounted armature, Figs. 1-3, comprises a non-magnetic cross-limb 1 enclosed in rubber sleeves 6 clamped between steel yoke members 7, 8. The cross-limb 1 carries a vertical limb 2 of magnesium adapted to carry a steel needle 3 secured by a clamping screw 4. The needle co-operates with an air gap between steel pole plates 11, 12 below permanent magnets 9, 10 arranged on either side of a fixed coil 17. All the parts are secured together by screws 20 entering a magnesium block 18, which itself is held in a pick-up arm by screws 33. Leads from the coil pass through and between insulating plates 24, 25 to pins 28. By reversing the unit comprising members 7-12, the transducer is adapted for taking a bottommounted armature, Fig. 4, the upper end of the needle oscillating in the air gap between plates 11, 12. Figs. 5 and 6 show modifications in which the vertical limb of the armature member is made of steel, the top end being flattened in Fig. 5 to lie in the air gap, while the plates 11, 12 are rounded off in Fig. 6 to prevent " freezing when the assembly is slightly off-centre. In the modification of Fig. 7 the armature is held in rubber sleeves clamped between brass blocks 57, 58, held between T-shaped pole pieces 50, 51 to which are secured polar extensions 52, 53 with pole tips 54, 55, hidden from view in Fig. 7 by brass inserts 68, Fig. 10 (not shown). The magnetic system is completed by a horse-shoe magnet 56. The polepieces and polar extensions can be inverted, Fig. 9, for use with a bottom suspension armature. The armature member shown in dotted lines in Fig. 11, can be used in either upper or lower suspension mode and the rubber sleeves 74 may be subjected to radial compression as described in Specification 611,184.