GB507697A - Improvements in loud speaking telephone systems - Google Patents

Abstract

507,697. Loud-speaking systems. MAGNETA TELEPHONE. April 13, 1938, Nos. 11413 and 11414. Convention dates, April 13, 1937 and April 7, 1938.[Class 40 (iv)] Howling of a loud-speaking system is prevented by providing independent circuits for the two directions of speech and A.V.C. in the amplifier of at least one of them. The amplifiers may be associated with the loud-speakers or may be at a central point, e.g. a small automatic exchange. Automatic exchange system with only one connecting link. A subscriber such as A2, Fig. 6, initiates a call by operating the right-hand set of springs of a key E. Lamps 26, 27 light at the calling station and lamp 27 at all the other stations. Ground is connected to wire 25 to step the call finder 17 off-normal, and ground is removed from the calling subscribers's terminal in the f bank to cause the finder to stop on his terminals. The subscriber then dials at DA2 to step the final selector switch. The called subscriber answers by operating the lefthand springs of his key E to connect up his microphone and light lamp 26. When the calling party restores his key, both switches go home by self-interruption. The switches are of the back-stroke type and their selfstepping circuits include contacts controlled by the ratchet wheels for ensuring a complete step at each interruption. Sluggish relays 23, 24 keep the amplifiers C1, C2 disconnected during stepping and 23 also controls the final selector homing circuit. Modified system, Fig. 7, with two links. Each subscriber has a separate key and busy lamp for each link. The key contacts, except those controlling the busy lamps, are multipled however and it is thus necessary to have a modified starting arrangement for the callfinder. When A5, for example, throws key E, the finder driving magnet is energized initially over off-normal springs 291 and subsequently over a front contact of 23. When the switch stops, the relapse of 23 puts ground from an off-normal contact 292 onto the calling party's f terminal to mark him busy to the other finder. A relay 28 prevents this ground from affecting the finder shown until the calling party hangs up. The Specification as open to inspection under Sect. 91 comprises also an arrangement, Fig. 5 (Cancelled), in which the normal instruments are associated by means of an anti-sidetone circuit and the receiver is shunted by the input transformer of the loud-speaker amplifier, the first valve of which is subject to automatic volume control by means of a back-biassing circuit 3, 5, 6. This subject-matter does not appear in the Specification as accepted.