Patent GB-790751-A (GB)
Title: Improvements in or relating to gramophones
Inventor: COSTA HARRY DA
IPC: G11B3/085
Filed: 1953-09-17
Abstract: 790,751. Gramophone tone arm positioning and turntable motor control devices. PLESSEY CO., Ltd. Sept. 13, 1954 [Sept. 17, 1953], No. 25718/53. Class 40 (2). A gramophone tone arm positioning device for selectively moving the tone arm 2 to one or another of a number of positions, according to the diameter of a record on the turntable 5, whereby in each case to engage the stylus with the commencement of the sound-track groove, has the positioning movement of the tone arm terminated by a stop-plate 16, the selective setting of which is automatically determined by the upward stroke of a feeler member 13 having contact surfaces 14, 15 at different levels for respective engagement or not with the edge portions of records of three different diameters to terminate the upward stroke of the feeler member at different points according to the record diameters. As shown, manual depression of a lever 3, Fig. 4, not shown, pivoted on a fixed pin 3b, causes by engagement of a slot 3a in the lever with the arm 6a of a cam 6, Figs. 3 and 5, tilting of the latter whereby a nose 6c of the cam co-operates with a shoulder 7a of a platform 7 to lift the latter. The rising platform lifts the tone arm 2 from its rest position until the stylus is above the height of the record surface whereupon the nose 6c reaches a circular edge 7c of the platform which platform then stops rising. Fixed to the platform 7 is a pin 7b which, when the platform rises, pivots, through the resilience of a spring 19b, a lever 19 about its pivot pin 20, and a fulcrum pin 22 at the other end of the lever lifts a balance lever 17 to the respective ends of which are pivoted the feeler member 13 and the stop-plate 16. Due to their relative weights initially the feeler member 13 rises until its contact surfaces 15 or 14 abut the edge of a 12 or 10-inch record respectively, or neither surface abuts the edge of a 7-inch record, and following such variable rising movement complementary residual movement of the balance lever 17 raises the stopplate 16 to a respective position in the path of one of three abutment surfaces 18, 25 or 28 on the tone arm 2 and which correspond to 12, 10 and 7-inch records respectively. During tilting of the cam 6 a roller 10 carried thereby engages a slot 9 in a pusher lever 8 which starts to pivot anti-clockwise about the fixed pin 20 when the nose 6a reaches the end of shoulder 7a, and its top engages an abutment plate 11 of the tone arm 2 to swing the tone arm towards the record until the tone arm is stopped by one of the surfaces 18, 25 or 28 engaging stop-plate 16. Lever 3, when manually released, lowers the tone arm with the stylus correctly positioned to engage the commencement of the sound groove. A projection 11a on the tone arm engaging an appropriate notch 12 in the top of platform 7 increases the precision of the positioning operation. The lever 3, when depressed, also pivots about the pin 3b, Fig. 4, not shown, a lever 4 which switches on the gramophone motor, not shown. Specifications 790,752 and 790,753 are referred to.