Patent GB-468137-A (GB)
Title: Improvements in gramophone and the like sound reproduction devices
IPC: G11B17/02
Filed: 1935-09-26
Abstract: 468,137. Gramophones. WILKINSON, R. Sept. 26, 1935, No. 26596. [Class 40 (ii)] Relates to an automatic device for closing the control circuit of an electric motor whenever the rate of progression of a gramophone tonearm over a record differs from a normal predetermined rate, having one contact of a switch in the control circuit carried by an arm coupled frictionally to a part moving with the tone-arm and a second contact adapted to co-operate therewith. According to the invention, the arm carrying one contact is moved away from the second contact by the tone-arm during normal progression over the record and is automatically moved back at predetermined intervals of time towards the second contact, which has then been moved temporarily out of range of the arm, the contacts only coming into engagement when the tone-arm fails to be displaced, as when the stylus enters a terminal concentric groove on the record, and thus allows the second contact to come into the range of the contact on the arm. The control may be effective to stop the turntable motor or to return the tone-arm to its starting position. As shown, the turntable spindle 1 is in geared connection of any desired ratio with a control disc 2 so as to give a slow motion of rotation in an anti-clockwise direction to the disc. This disc carries a pin 3 adapted to co-operate with one end of a lever 4 so as to displace the latter about its pivot 5 against the action of a spring 25. An arcuate frictional shoe 6, pivoted at 7 to the other end of lever 4 and carrying by means of an arm 12 a contact 18, is adapted to be turned about its pivot by a corresponding arcuate friction member 8 rigidly mounted on a bracket 9 on the tone-arm 10 so that, as the tone-arm moves across a record, the contact 18 is gradually moved away from a second contact 17. This contact is carried on the end of one arm 19 of a pivoted bell-crank lever 20, the other arm of which carries a roller 21 pressed by a spring 23 into contact with a cam 22 on the disc 2. The cam 22 is provided with a cut-away portion 24 into which the roller 21 is drawn during a certain portion of a revolution of the disc 2 so as to bring contact 17 temporarily into the range of movement of the contact 18. During the playing of a record, the pin 3 co-operates at predetermined intervals with the lever 4 so as to move the shoe 6 out of engagement with the member 8, a second pin 16 subsequently co-operating with an arm 30 on the shoe so as to return the arm 12 to its initial position against a stop 26, the contact 17 having been moved at this particular time by the roller 21 and cam 22 temporarily out of range of the arm 12. When, however, the stylus enters a concentric groove at the end of the record, the arm 12 is no longer moved away from its stop 26 and as soon as the roller 21 drops into the cut-away portion 24 of cam 22, contact 17 moves into engagement with contact 18 so as to complete the circuit of relay 15. Energization of this relay releases the spring- controlled hand lever 45 so as to bring the contact 46 carried thereby on to the insulating segment 28 and thereby open the circuit of the turntable motor 44. In order to allow the control to become effective when a record having an eccentric terminal groove is being played, a third contact 14 is provided on the arm 19 towards which a contact 13 on the arm 12 is gradually moved as the tone-arm progresses across the record, the arm 12 being set back at predetermined intervals as before by the action of the pin 3 and the contacts 13, 14 only coming into engagement on the increased angular movement of the tone-arm due to the stylus entering the eccentric groove. Means are described, Figs. 3 and 4 (not shown) whereby the coupling between the shoe 6 and member 8 is held disengaged so long as the tone-arm is maintained in a raised position above the record. A master switch in circuit with the contacts 17, 18 and 13, 14 and actuated by a pin 51 on the tone-arm prevents operation of the control 6, 8 from becoming effective until the tone-arm has moved a predetermined radial distance. If desired, the disc 2, instead of being in geared connection with the turntable spindle, may be driven by an independent motor.