Patent GB-552019-A (GB)
Title: Improvements in or relating to photo-electric pick-ups for phonographs
IPC: G11B7/00
Filed: 1941-09-16
Abstract: 552,019. Phonograph pick-ups. PHILCO RADIO & TELEVISION CORPORATION. Sept. 16, 1941, No. 11845. Convention date. Sept. 18, 1940. [Class 40 (ii)] [Also in Group XL] A photo-electric phonograph pick-up is enclosed in a casing forming a compact pickup head 3 and this head is mounted on a single swinging supporting arm. The pick-up comprises a lamp assembly 29. Fig. 2, a lightsensitive cell assembly 30, and a stylus oscillated mirror device 31, all mounted on a base plate 4 and enclosed by a translucent cover. The lamp 71, Fig. 19, is provided with a conventional socket 72 mounted in a resilient sleeve 73 which can be adjusted slidably and rotationally in one end of an enclosing tube 52, the other end of which contains lenses 67, 68 spaced apart and held in place by sleeves 69, 70. The lamp has a line filament 74, Fig. 20, and the lens end of the enclosing tube has a corresponding rectangular aperture. The enclosing tube is also formed with apertures above and below the lamp to illuminate the translucent cover and the sound record near the stylus. These apertures also serve for ventilation in conjunction with apertures in the cover. The tube 52 containing the lamp is attached to lugs 62, 63, Fig. 2, on a bracket 53 adjustbly gripped by pins 54, 55, 57 passing through slots in the bracket and fastened to the base plate 4. The bracket is adjusted by means of a screw 59 with a tightening spring 61. The slots in the bracket are such that the bracket in effect rotates about the axis of the mirror when adjusted by the screw 59, which passes through a lug 60 on the plate 4. The light sensitive cell may be a selenium cell, or, as shown, a barrier layer cell 78, Figs. 21 and 23. The cell is gripped between a back insulating piece 77 and a front terminal conductor 79 by a spring 84, which acts also as back terminal. The conductor 79 has ribs 82 to engage the front face of the cell and top and bottom lugs 80 which are bent to engage the back of the insulating piece 77. This assembly is mounted in a bracket 75 fastened to the base plate 4. The conductor 79 extends over the front of the cell forming an opaque edge serving to modulate the amount of light striking the cell when the mirror is oscillated. The stylus oscillated mirror device, Figs. 2, 11, and 14 comprises two plates, 33 34 fastened against each other to a lug on the base plate 4 to form top and bottom bearings 40, 41 for the spindle of the oscillating mirror 39. The bearings are lined with resilient material. The upper bearing is cylindrical. The lower bearing is of square section to locate the neutral position of the mirror: The stylus is a sapphire 47 fastened by a hollow rivet to a crank arm 46 attached to the lower end of the mirror spindle. A damping vane 49 of a nitrocellulose plastic such as "viscaloid" is attached to the upper end of the spindle. The torsional resilience of the crank arm 46 and the masses and resiliences of the other parts of the vibrating system produce a resonance at the upper end of the acoustic scale which compensates for the drop in response of the photo-electric device. Further compensation can be introduced by the amplifier connecting the cell to the loud-speaker. The translucent cover 7, Fig. 4, is of moulded material and is provided with a button 9 also of translucent material but of a different colour. The button 9 is attached to a spring 10 pivoted at 11 to enable the button to be depressed and swung aside to allow direct vision of the photoelectric device for initial adjustments. The pick-up arm 1, Figs. 2 and 3, is shaped as shown and is mounted by a bracket 13 on an horizontal pivot carried by a sleeve 15 attached to a vertical shaft 16 mounted in a ball bearing 21. The sleeve 15 is tightened on the shaft 16 by means of a screw 20. The bracket 13 is attached to the pick-up arm by means of a plate 12 formed with a slot along which a balance weight 23 can be adjusted. The weight 23 is attached to a member 24 formed with ears 26 adapted to ride over the edge of the slot in the plate 12.