Patent GB-323027-A (GB)
Abstract: 323,027. Graham & Co., Ltd., A., Rickets, W. J., and Stott, W. Sept. 19, 1928. Manual exchange and direct-call systems.-In systems in which a buzzer at an exchange or other point between two stations actuates the telephone receiver at the called station, the reply of the latter stops the buzzer. Two exchange systems, a system which is primarily a directcall system but can be used as an exchange system, and a two-station direct-call system are described. In the last-mentioned system, if the call is not answered, the buzzer is cut off after a predetermined time and the calling station who receives a tone signal while calling is in progress may speak over the line, his remarks being given out by a loud speaker which is disconnected when the called party removes his handset. 1st exchange system Fig. 1. When subscriber X calls, his line relay d operates calling signals u, w, the latter of which is disconnected when the operator plugs in. The operator throws key K to operate the set of springs associated with the plug she has used for answering and relay 9 pulls up over the loop and connects up her telephone set the buzzer 10, the self-interrupting contacts of which are cut off acting as a feed choke. She then plugs into the wanted line and throws the key the other way whereupon 9 falls back and connects up the buzzer 10 in a selfinterrupting circuit to light the lamp z and produce an audible signal in the receiver b at the wanted station. When the called party replies, 9 pulls up over the loop and cuts off the buzzing contacts. Lamp u<1> lights and the operator restores the key. 2nd exchange system Figs. 2 and 3. The cords are provided with a sleeve conductor over which, when the operator plugs into an idle line and operates the key springs associated with the plug, a relay 17 pulls up and connects up a buzzer 26. When the called party replies his line relay 31 releases 17 which connects up the operator's set. The same cord is used for inter-office calls, both offices having the same battery. When the operator plugs into a junction jack 42 and throws her key, a circuit is made over 17 and the upper wire of the junction for 31a at the distant office to light lamp u<1> and operate an audible or other signal w. 17 does not pull up in this circuit and buzzer 26 therefore does not operate. When the operator answers, this circuit is broken at 45 and the operators and subsequently the subscribers converse over both junction wires and the condensers 44 in parallel. Direct call system Fig 4, with main and subordinate stations and operable as an exchange system. The equipment at the main station resembles that at the exchange in the 2nd system described above but there is only one key which is associated with a particular cord by plugging the latter into a jack 48 the other plug being used for answering or calling a subordinate station or, by plugging into a jack 42, another control station or an exchange. The cords may be used for interconnecting subordinate stations. Two-station direct-call system, Fig. 5. When station Y calls, his relay 51 pulls up and makes a self-interrupting circuit for the relay 51 of the other station which vibrates its lower armature to give a buzzer call at X but is unable to pull up its heavy upper armature until the subscriber at X replies. If he fails to do so. a thermal relay 60 breaks the buzzing circuit and the subscriber at Y who has heard the call signal over the small condenser 59 (which may be replaced by a resistance) may now talk over the line to the loud speaker 58.