Patent GB-247810-A (GB)
Title: Improvements in or relating to gramophones and like machines
IPC: G11B19/28
Filed: 1925-05-29
Abstract: 247,810. Polden, C. E., and Tozer, B. E. May 29, 1925. Speed regulating. -Relates to gramophone and the like such as are described i n Specification 206,779, in which means are provided for producing constant linear velocity of the record track under the stylus. According to the invention, in order that different linear velocities, suited to different records, may be produced, interchangeable cams are provided, the function of any one cam, when in operation under the control of the tone-arm being to act upon the governor of the motor. Means are also preferably provided, in addition, for manually adjusting the cam which for the time being is in use, to obtain small variations of the tracking speed. In the construction shown in Figs. 1, 3 and 4, a member d adapted to be connected by a link e to the tone-arm (not shown) is pivoted upon a boss o on a plate p which is pivoted at q to a base-plate a. The boss o is eccentric to the pivot q. Pins f project upwardly from the part d and engage in holes in any one of a set of detachable cam plates such as h, the cam being held in place by a leaf spring m. When a cam is in position as shown in Fig. 1, an arm c projecting from the governor mechanism engages against it, and as the tonearm moves during the playing of a record the link e rotates the part d and thereby shifts the cam; the edge of the cam is so shaped that the arm c, moving under its control, varies the angular speed of the record in the desired manner. When a different record is played, the cam h may be removed and replaced by another of appropriate formation. An arm r extends from the plate p over a scale s, and is shown in Fig. 1 as set in the normal position for a constant linear speed record. Small variations from the normal in the starting speed may be made by displacing the arm r on either side of the neutral position shown, thereby effecting a slight initial displacement of the cam with respect to the fixed pivot q. To use the machine with ordinary records (i.e. running at a constant angular speed), the cam h is removed and/or the link e is disconnected, and the pointer r is moved so as to be over a second set of graduations on the scale s, as shown in Fig. 4. In this position, a cam t, integral with the plate p, determines the position of the arm c, which remains fixed, in accordance with the setting of the pointer r, for the duration of the playing. Cams of different formation from that shown, e.g. slotted cams, may be used. Figs. 8 and 9 show a modification in which, instead of separate detachable cams, a single plate 25 is provided, having separate independent cam surfaces 26, 27, 28 on its edge. The plate 25, mounted on a spindle 21, is adapted to be connected to an arm 20 operated by the movement of the tone-arm. The arrangement is such that the connection of the parts 25, 20 can be altered so as to bring any one of the cam surfaces, as desired, into position for acting upon the governor-controlling lever c. Provision is also made in this construction for independent variation of the initial speed, and for bringing a separate cam 17 into action when the machine is to operate with ordinary records.