Patent GB-530068-A (GB)
Title: Improvements in sound reproducing apparatus
Filed: 1939-06-15
Abstract: 530,068. Optical sound reproducing apparatus. KOLB, O. K., and TOMES, R. A. June 15, 1939, No. 17504. [Class 40 (ii)] An optical sound reproducing apparatus comprises a rotatable drum carrying one or more helical sound record tracks and one or more circular sound record tracks and a pickup system having a movable sound head housing selector mechanism co-acting with retractible push-buttons and fixed pins permitting selective reproduction from any one of the tracks. As shown in Fig. 1, a cylinder 1 carrying a circular track T1 and a helical track T2 is driven through bevel gear 8 by a motor M, and motion is transmitted by a chain 5 to a lead screw 4. The pick-up 2 comprises two casings SH, SM. The casing SH contains a photo-electric apparatus and is guided by rods 3 along the cylinder 1. The casing SM is vertically slidable against the side of the casing SH and is normally held up by a spring E, Fig. 5, so that a part nut 38 at the bottom of the casing is away from the lead screw 4. The casing SM carries three external cams 28, 33, 36 and an external handle 21. Inside the casing SM, a sector 23, Fig. 4, fast with handle 21 has a shoulder 24 co-operating with a lug 25 on a fork 29 fast with cam 28 and engaged with a pin 30 on a cranked lever 31 fast with cam 33 and adapted to operate a lever 34 to close contacts C, C1 in the pick-up circuit.. The cam 36 co-operates with the switch lever 34, and a spring B is provided to return these parts to normal position. A panel P, Figs. 1 and 7 extends alongside the lead screw 4 and is fitted with a fixed button 10 3  and two spring controlled buttons 10 1 , 10 2 . Each button 10 1  or 10 2  has a body part 46 with an extension 45 forming a shoulder 47 for the control spring 48. The body part has a collar 49 co-operating with projections 40 on a lever 39 pivoted at 42 and urged by a spring T in the direction of the arrow D, whereby a button when depressed is held depressed, and the depression of any button causes the release of any other button previously held depressed. These buttons co-operate with the cams 28, 33, 36 as explained below. To use the machine. the button corresponding to the track desired is depressed, say the button 10 2  for the track T 2 , the pick-up is then moved along the guide rods 3 to near the start of the track T  2  by means of an endless band 50 on pulleys 51 driven by a handle H. The casing SM is now pressed down to engage the nut 38 with the lead screw 4, and is held depressed by a pin 52 on the sector 23 coming under a shoulder 53, the sector being turned by a spring. As the pick-up is moved forward by the lead screw, the cam 33 is rocked by the button 10 2  and the switch contacts C, C 1  in the pick-up circuit are closed. When the scanning of the track is completed, the cam 28 is rocked by the fixed button 9 causing the opening of the contacts C, C 1 . The handle 21 may now be turned to allow the casing SM to rise and disengage the nut 38. For scanning a circular track T 1 , no fixed button is required, the spring controlled button 10 1  is depressed and rocks the cam 36. Record-The record tracks which may be produced as described in Specification 423,505 are in the form of strips fitted in grooves in the cylinder 1, which may be of aluminium, magnesium or wood and may reflect the light back through the track strip. Optical reproducing device.-The optical pickup shown in Fig. 2 comprises a lamp 12, a slit 18 and lenses 13, 13 1  for projecting light on the record drum 1. The light reflected from the record track or from the cylinder through the record track is directed by mirrors 17, 19, 19 1  to a photo-electric cell 14. A lens system may be added to concentrate the light on the cell. These parts together with a first-stage amplifier V are contained in the casing SH.