Patent GB-462195-A (GB)
Title: Improvements in and relating to the reproduction of sound from record films
IPC: G11B7/00
Filed: 1935-11-14
Abstract: 462,195. Optical sound - reproducing apparatus. KOLB, O. K. Nov. 14, 1935, No. 31514. [Class 40 (ii)] [Also in Group XL] Relates to apparatus for the optical reproduction of sound films alternatively from films either of the asymmetric type requiring for their reproduction the use of two light-sensitive elements or from films of the normal type and consists in the provision of electrical circuitchanging elements operable at will to adapt the photo-electric reproducing equipment to operate with one or other of said types of film. Fig. 1 shows an arrangement in which the pencil of light A after passing through the film C is divided by the lenses DA, DB and focused thereby on to the cathodes PA, PB of a photoelectric cell P having an anode PC. For reproduction of an asymmetric type of film, the cathode PA is connected to one end TA and the cathode PB is connected by a switch arm S to the other end TB of the centre-tapped primary winding of the push-pull transformer T whilst, for reproduction of a normal type of film, the arm S is moved on to contact SA so that both cathodes are connected to the terminal TA. According to a modification, Fig. 2 (not shown), the cathodes are connected to a coupling resistance or inductance instead of to a centre-tapped transformer winding and a second switch arm may be provided whereby the negative feed serving the cathodes may be connected either to a centre tapping on the resistance or so as to bring the whole resistance into series with the two cathodes. Fig. 3 shows an arrangement in which the cathodes PA, PB are connected to the two symmetrically disposed halves of the primary winding of a transformer T, the cathode PA being connected to the junction TA whilst the cathode PB and centre tapping TC are connected to half the primary winding through the change-over switch S. For the reproduction of an asymmetric type of film the windings are connected in opposed phase as shown whilst for reproduction of a normal type of film the switch is thrown over so as to connect the windings in phase with one another. According to a further modification, Fig. 4 (not shown), each cathode is connected to a separate transformer, the secondary winding of one of which is arranged in circuit with a change-over switch by means of which a reversal of direction and of phase of the output of the corresponding cathode can be effected. If desired, the bicathodic type of cell shown may be replaced by separate cells and arrangements are also described in which selenium cells or rectifier cells of the cuprous oxide type are employed. Thus, as shown in Fig. 5, two selenium cells PD, PE have one extremity each connected through a common junction EC to one terminal of a battery E, the other terminal of which is connected to the centre tapping TC of the primary winding TP of the transformer T. The other extremities of the cells are connected one to the junction TA and the other to the switch arm S as shown. Fig. 6 shows a modification of the arrangement in which the cathodes PA, PB are connected to a coupling resistance R. As shown, this resistance is connected through coupling condensers KA, KB to the control grids of two valves VA, VB which are connected in push-pull to the split primary winding of a transformer and a switch S is provided to change the anode connection of one of these half windings from the in-phase connection for normal films to the push-pull opposed phase connection for asymmetric films. A modification of the arrangement shown in Fig. 1 is described, Fig. 7 (not shown), in which the switch arm which connects both cathodes in push-pull for the reproduction of asymmetric films is adapted to break the circuit of the cathode PB to the transformer winding when normal films are to be reproduced.