Patent GB-399231-A (GB)
Title: Improvements in and relating to electrical reproducers or pick-ups for gramophones
IPC: G11B3/46
Filed: 1932-04-05
Abstract: 399,231. Gramophone pick-ups. MACKIE, D. M., 25, Denbigh Place, Victoria, and MACWILLIAM, A., 17, Rural Way, Streatham, both in London. April 5, 1932, No. 9774. [Class 40 (iv).] Relates to a gramophone pick-up embodying a single armature mounted on a stylus arm and adapted to vibrate in front of the poles of an electromagnet. According to the invention, the stylus arm is supported on two oppositely disposed pivots in such a manner that it is free to rock in one plane only and means, acting on the stylus arm and adjustable from the exterior, are provided adjacent the pivotal axis of the arm for positioning the armature relatively to the magnet poles. Fig. 2 shows the invention applied to an existing earphone in which a two-part box-like structure 1, 2 is carried by a plate 3 attached to a circular plate 4 adapted to replace the usual earpiece diaphragm. A bent stylus arm 6 carrying at its upper end a flat plate,armature 8 is pivoted at 9 on oppositely disposed set pins passing through the side walls of part 1, the part 7 of the arm being damped by a felt-lined saddle piece 11 smeared with petroleum jelly and carried by the part 2. Alternatively, the part 2 can be filled with petroleum jelly in which case the saddle piece may, if desired, be omitted. The position of the armature relatively to the pole-pieces 15 is adjusted by two screws 14 bearing against a metal plate 13, one above and one below the pivot point 9, the plate 13 bearing against a pad 12 of felt, spongy indiarubber or metal spring disposed against the face of the vertical par of the arm 6. When the device is to be applied to an earpiece designed to operate when its diaphragm would normally be in an approximately vertical position, the part 7 of the arm is formed continuous with the remainder as shown in Fig. 5, so that the needle 5 and armature 8 are in parallel planes, the arm 6 projecting through the end wall of the part 1 and the needle securing screw 20 being arranged at the front and engaging in a rib 21 on the arm. In this modification, the felt &c. pad 22 is arranged on each side of the rib 21, a metal plate 23 and two adjusting screws 24 being provided as previously described. In order to enable the armature to be disposed above or below or to one side of the mid-axis of the poles 15, a pair of plates 25 having poles 26 may be secured as shown to the face of the plate 3 adjacent the poles 15, the poles 26 projecting through slots in the plate so as to co-operate with the armature. Fig. 10 shows a modified method of pivoting the stylus arm and of securing the needle therein in which the left pivot consists of a threaded sleeve 27 secured by a lock nut 28, the needle securing screw 29 passing through the sleeve and the rib 21 being dispensed with. Figs. 13 and 14 show a further modification in which the pick-up is formed as a single complete unit, the stylus arm, armature and associated parts being arranged substantially as in Fig. 10 with the exception that a piece of felt &c. may be provided in the space 29x as well as at 30. In this construction, the plate 3 and its component parts are secured by bolts 37 to a plate 32 to which the core 31 of the electromagnet is also secured, the plate 32 being secured to a lug 34 on the back plate 35 of the main casing 36 whilst the box-like part 1 is supported in the casing by an arm 38. The casing 36 is formed with a boss 39 by which it is pivoted to the swinging arm 40 of the gramophone. In all constructions, the stylus arm may be.formed of a very light metal, such as aluminium.