Patent GB-441479-A (GB)
Title: Improvements in or relating to automatic control apparatus for acoustic recording and reproducing apparatus
IPC: H01H47/24
Filed: 1934-07-13
Abstract: 441,479. Sound-reproducing apparatus. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Electra House, Victoria Embankment, London, and TWEED, C. J. F., Hursley, Honiton, Devonshire. July 13, 1934, No. 20620. [Class 40 (ii)] [See also Group XL] Relates to devices for automatically controlling the starting and stopping of soundreproducing apparatus, particularly applicable to advertising or announcement apparatus adapted to be set in action by the interruption of a beam of light or infra-red rays, &c., and to be stopped automatically when an announcement is completed. Among other applications of the invention, it could be used for reproducing recorded news bulletins &c. when the apparatus is started by reception of a special signal dialled by a telephone subscriber. The invention comprises a special combination of relays, one of which completes a circuit through an electromagnetic device to render operative the driving means of the sound-reproducing apparatus (which may be a telegraphone), after another relay has been actuated upon the interruption of a light beam or the receipt of a predetermined signal ; two other relays are operatively associated with valves which are controlled through different time-constant circuits by the output currents from the sound-reproducing apparatus so as to act successively and, after causing the driving-means to become inoperative, the relays are automatically reset to their normal condition. In the apparatus shown, a telegraphone steel tape record 1 is adapted to be driven past magnets 7, 6, 5 provided respectively for obliterating, recording, and reproducing. The driving pulley 4 is continuously driven, and drives the tape 1 when an endless friction belt 8 is drawn taut into engagement with the tape by means of a jockey pulley 11. This pulley is carried by the armature of an electromagnet 16, and is actuated to render the telegraph one drive effective when the magnet 16 is energized on the closure of the contacts 19, 20 of a relay 17. The windings of the relay 17 are in the anode circuit of a valve 25 (constituting a second relay), the grid of which is connected to a photo-electric cell 31, a circuit through which is normally closed through a second pair of contacts 20, 30 of the first relay 17. The cell 31 is normally illuminated by a lamp 32, and in this condition the valve 25 is so biassed as to be non-conductive. When the light beam is interrupted, the grid bias of the valve 25 changes, and current passes through the valve, energizing the relay 17, which thereupon closes the contacts 19, 20, so that the sound-reproducing apparatus is started. At the same time, the contacts 20, 30 in the circuit of the cell 31 are opened. In parallel with these contacts are a pair of normally open contacts 36, 37, controlled by a third relay 38, the windings of which are connected to the contact 40 (in a fourth relay 42) which is held away from a contact 41 by the energization of the coil 42. The windings 38, 42 are associated with double-diode-triode valves 45, 49, which are so biassed by batteries 62 that the diode portions are normally non-conductive, and the triode portions are conductive. Each battery 62 is connected to one'of two secondaries 55, 53 of a transformer 52 to which amplified audiocurrents are supplied when the reproducer 5 is in action. Connected between the grid and cathode of each valve 45, 49 is a resistanceshunted condenser combination T<1> or T2, the circuit T<1> having a smaller time constant (e.g. 1À25 seconds) than that of the circuit T<2> (e.g. 1À4 seconds). When the telegraphone is running, and audio-signals of sufficient magnitude are supplied from the reproducer 5 through the transformer 52, the diode portions of the valves 45, 49 become conductive, and the anode circuits of the valves cease to pass current. Consequently, the contacts 40, 41 close, but contacts 36, 37 remain open. Shortly after the sound-reproduction has finished, the triode portion of the valve 45 becomes conductive, current passes through the contacts 40, 41, and the relay 38 is energized. Thus, the contacts 36, 37 are closed, so that the photo-electric cell 31 (if still illuminated) puts the valve 25 out of action, so de-energizing the first relay 17 and stopping the drive of the telegraphone. A little later, the triode portion of the valve 49 becomes conductive, the relay 42 is energized, and the contacts 40, 41 are opened. Thereupon, the relay 38 is de-energized, the contacts 36, 37 are opened, and the whole apparatus is thus reset for a new operation. If there is a joint in the telegraphone wire, it must be so arranged that it does not pass under the reproducer 5 during the "silent period," otherwise the valves 45, 49 will be prevented from functioning properly.