Patent GB-475788-A (GB)
Title: Improvements in electric pick-up mechanisms
IPC: H04R11/08
Filed: 1936-02-21
Abstract: 475,788. Phonographic reproducers. SYKES, A. F. Feb. 21, 1936, Nos. 5322/36, 3897/37, and 4038/37. [Class 40 (iv)] in an electric pick-up device, tor run-anadale sound-records, comprising a magnetic system held by a supporting structure against relative movement thereto, a stylus member carried by said magnetic system and free to move in a vertical direction relative to said system, means applying a substantially constant bias force between the magnetic system and the o stylus member to urge the latter towards the record surface and means actuated by vertical movements of the stylus member to convert said movements into electrical variations, the stylus member, together with or independently of said magnetic system, is capable of free movement in a horizontal direction relative to the supporting structure. In the arrangement shown in Fig. I ('5322/36), a supporting member 31, 32 secured to a fixed support 34 carries a bracket 99 on which is pivotally supported a vulcanized fibre block 100 carrying a magnet 4 co-operating with polepiece members 101, 102. A central polepiece 11 attached to the member 101 carries the voice coil winding 10 and is associated with an enlarged portion formed on an armature 7 pivotally mounted at 103 on the polepiece 102. The armature 7 is urged towards the record 42 by an adjustable spring 104 and the pivot members determining the axis 36 for the block 100 are adjustable. In a modified construction, Figs. III and V (3897 /37) the permanent magnet 4 mounted in a casing 78 of moulded material has a central pole member 11 formed with a chamfered tip and a composite polepiece extension formed by members 108, 109, 110. A strut 23 may be screwed to the extension piece 109 and engage the magnet 4 either directly or with the interposition of damping material 114, such as boiled castor oil. The magnet assembly is rotatable on a vertical axis 36 by means of a pin 116 formed on a gunmetal nut 123. which clamps the magnet 4 to the polepiece extension 108 and an adjustable bearing 117. The armature 7 pivotally mounted on the polar extension 110, is attached to a stylus member 111 formed with an extension piece 113 to which the biassing spring 104 is attached. The stylus member which is of channel form and is cut away at 112 carries a stylus 8 and engages with a wire loop 43 by which its movement is limited and guided. The tension of the spring 104 may be adjusted by the movement of an arm 105 secured to the polar extension 110 which itself is adjustably carried by the member 109 in order that the distance between the armature 7 and the polepiece 11 can be varied. The oscillations of the spring 104 may be damped by a coating of petroleum jelly and in addition the space 122 may be filled with this substance. The armature 7 has a rounded end to engage a similarly shaped recess on the member 110 and is supported by pivots comprising a bush 120 and a gunmetal insert 121. The leads from the coil 10 are taken to soldering tags 82 directly connected to terminals on the outside of the casing 78. A modified construction of armature and stylus lever is shown in Fig. IV (3897/37) in which the armature 7 is milled out at 118 and is soldered to a V- shaped strip 111 which carries the stylus 8 and has a projection 119 to engage the wire loop 112 described in connection with Fig. III. In a further construction, Figs. I, II, (4038/37), the stylus member 111 is mounted on a squared trunnion 129 freely rotatable on a vertical axis 124 on pins 126, 127 carried respectively by the armature 7 and a U-shaped strap 125 connected to a spring 104 adjustably mounted by a member 105. The magnet 4 is moulded in the casing 78 and one polepiece is formed by a member 110 slotted to engage with stampings 6 associated with the magnet. In the adaptation of the apparatus to actuation means of the moving-coil type, the V-shaped stylus member 111, Fig. IV (3897/37) and Fig. II (4038/37) is located in a V-shaped gap between opposed polepieces and forms the conductor for the speech currents corresponding to the vibrations of the stylus. Specifications 243,395, [Class 40 (iv)], and 439,800 are referred to.