Patent GB-116163-A (GB)
Title: Improvements in and relating to Gramophones and the like.
Inventor: ARMSTRONG WILLIAM LESLIE
IPC: G11B3/00
Filed: 1917-06-09
Abstract: 116,163. Armstrong, W. L., and Bindloss, A. K. June 9, 1917. Tone arms; tone-arm joints; sound - boxes, mounting.-The length of a gramophone tonearm and the angular setting of the soundbox are determined by formulµ so that the stylus lies tangential to the record groove at two chosen radii of the record, preferably the innermost and outermost grooves. In order that the stylus may always lie tangential to the record groove, the length of the tone-arm, or the angular setting of the sound-box, may be varied as the stylus moves over the record. In the form shown in Figs. 1 and 2, the tonearm 1 has a telescopic end section 4 which has a curved outer end in which the curved neck 5 of the sound-box can slide, pivoted brackets 7 and a graduated scale being provided. The horizontal part 1 of the tone arm is pivoted on pins 14 to a vertical portion 15 which is itself pivoted at 16 to a horizontal ring 17 turning on ball or other bearings in a socket 18. The ring 17 has a roller 22 mounted beneath it and co-operating with a cam surface 23 in the socket 18, the cam being shaped to give such longitudinal movement to the tone-arm 1 as is necessary to cause the stylus 6 to lie always tangential to the record groove 10. The tone arm is initially adjusted so that its effective length L, i.e. the distance between the stylus point and the tone-arm pivot, is equal to #S<2>+Rr, where S is the distance from the turntable centre to the tone-arm pivot, and R, r are two record radii, preferably the greatest and least of the record grooves. The sound-box also is adjusted in position so that the sine of the angle between the line of the stylus, as seen in plan, Fig. 2, and the line representing effective length of the tone-arm, is R-r/2L. The cam track 23 may be mounted on a vertical bracket attached to the socket 18, or the roller may be in a vertical plane and co-operate with the upper surface of the cam track. The roller may itself be formed with a cam surface. The linkage shown in Fig. 8 may be employed for keeping the axis of the tonearm 1 parallel to itself as the vertical portion 15 is tilted. Two links 28 are secured to the tone arm 1 level with the pivots 14 and they are coupled by links 30, curved in plan view, to a pivot 31 on the ring 17, the pivots 14, 16, 31, 29 forming a parallelogram in elevation. The vertical portion 15 of the tone arm may be arranged to slide bodily under the action of the cam 23 instead of turning on the pivots 16. In the arrangement shown in plan in Fig. 12, the vertical portion 15 has a horizontal flange 34 mounted to slide between guides 35 secured to the rotatable ring 17. A link 37 is pivoted at one end 36 to the flange 34 and at the other end to a pin 38 which is normally held by a catch 40 but may slide along a slot 39 when the catch is removed. When the tone-arm swings during the playing of a record, the link 37 takes up an oblique position and draws the flange 34 backwards in its guides 35. If the tone-arm is swung beyond the record, an arm 41 releases the catch 40 and carries round the pivot 38, thus preventing the mechanism for being locked or strained. In another modification, shown in Fig 14, the vertical portion 15 turns in an ordinary socket 18, and the length of the tone-arm is varied by links 45 connected at one end to a lever 47 controlled by the cam surface 23 and at the other end to the telescopic end portion 14 of the tonearm. The links 45 may be connected to the sound-box neck 5, causing it to slide in the curved end of the tone-arm section 4. The sound-box neck 59 may be connected to the tone-arm 1, Fig. 18, by a hollow vertical pivot 57, and the link 45 may be attached to an arm 46 secured to the hollow pivot 57.