Patent GB-445860-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04M9/00
Filed: 1934-10-10
Abstract: 445,860. Exchange &c. systems. TELEPHONE MANUFACTURING CO., Ltd., Martell Road, West Dulwich, London, FLINT, J. G., Kenlyn, Station Road, Orpington, Kent, and RYALL, L. E., 52, Crescent Gardens, Eastcote, Ruislip, Middlesex. Oct. 10, 1934, No. 29061. [Class 40 (iv)] Amplifiers for use in systems in which some or all of the subscribers have loud-speaking receivers are associated with common apparatus such as exchange connecting apparatus or common connecting circuits in an intercommunication system. If all subscribers have loud-speakers, the amplifiers are connected permanently in the connecting circuit, but when some subscribers have ordinarv receivers the association of the amplifiers and /or the effective amplification is varied in accordance with the nature of the calling and called lines. In systems in which a number of substations are adjacent one another as in one building, each such substation may take into use as required one of a common local set of amplifying equipments. Circuits between substations and centrally arranged amplifiers may comprise two, three, or four wires. Manual exchange systems. A call from a loud-speaker substation S1, Fig. 1, is made by pressing key CK which lights lamp SL of a colour indicative of the type of line. The operator inserts the answering plug PL1 of a cord circuit CT1 having associated with it amplifying equipment LSCC1, and a sleeve relay SR switches on the power supply to the amplifiers. The amplification of the elements RA, GA in this equipment is suitable for conversation between a loud-speaker substation S1 and an ordinary subscriber OT1 or the operator OT, but when a connection is desired between two loud-speaker substations, a second cord-circuit CT2 with amplifying apparatus LSCC2 is connected in series with the first with the aid of a jack link JP1, JP2. The substation S1 comprises a lamp PL lit as long as key CK is closed and a key MK for cutting out the microphone M. Fig. 2 shows a modification in which the same cord-circuit and amplifying equipment is suitable for calls from a loud-speaker substation either to an ordinary substation or to another loud-speaker substation. For this purpose, normally-inserted pads AB, AC are controlled by sleeve relays B, C, the jack of each loud-speaker line having ground connected to the sleeve. The operator's set has a further pad AT in its circuit and the arrangement is thus such that when two loud-speaker stations converse no pad is inserted, when a loud-speaker station converses with an ordinary station or with the operator one pad is inserted, whilst when the operator speaks to an ordinary substation, two pads are inserted. A common sleeve relay A switches on the power supply. Automatic exchange systems. Loud-speaker substations have grounded contacts in the banks of extra wipers W4, 2W5 of finderconnector links L, Fig. 3. The finder switching relay FSR (not shown), operates relay X for a call from such a line and an amplifier circuit AE becomes associated with the link over a switch ACS. Relay P, also operated over wiper W4, cuts out pad AP and if the called line is also a loud-speaker line relay Q operates and cuts out pad AQ. If only the called line is a loud-speaker line, relay X operates in parallel with Q over wiper 2W5 and an amplifier circuit is connected as before, but P is unoperated and pad AP remains in circuit. If all amplifier circuits are busy when a call is made, a chain circuit over contacts tr3 causes a busy signal to be given. The extra wiper 2W5 might be eliminated by controlling relay Q over wipers of the register-marker R and the associating switch, all lines having loudspeakers being given a particular first digit. The wiper W4 might also be eliminated by giving loud-speaker substations a special means of access to the register R or by placing relay X under the control of the calling substation, for example, by using a differential relay connected in series with the line relay. System employing a local group of amplifying equipments, Fig. 6. A subscriber having obtained connection over a lead L to some other subscriber by means of his ordinary instruments TS hangs up and presses key K2 causing relay S to connect up the stepping magnet MG of a hunting switch W1 .. W8. When an idle amplifying equipment AE is reached, relays T, A operate and TA operates in series with the magnet to switch through to the amplifier and to light lamp CL. If all equipments are busy, the switch moves to its last terminals at which relay B operates to connect up busy tone and to light lamp BL. Modified substation circuits. The substation circuit of Fig. 1 may have the loud-speaker and microphone interchanged, or the hybrid coil HB may be dispensed with, the microphone and loud-speaker being associated with the line through separate windings of a 3-winding transformer. In a further modification, Fig. 11, the arrangement is such that a line marked at the exchange as a loud-speaker line may use an ordinary handset without change of the exchange amplifying characteristics, a pad A being automatically connected in circuit when the handset is off the hook SH. Specifications 415,767, 416,372, 430,158 and 430,567 are referred to.