Patent GB-390868-A (GB)
Title: Improvements in telephone systems
IPC: H04Q3/58
Filed: 1931-10-20
Abstract: 390,868. Automatic exchange systems. AUTOMATIC ELECTRIC CO., Ltd., Strowger Works, Liverpool. Oct. 20, 1931, No. 29137. Convention date, Oct. 24, 1930. [Class 40 (iv).] In a system employing local transmitter feed batteries, these batteries provide the dialling potential, the impulses being repeated by thermionic valves to set selectors of usual bi-directional type. Calling is effected by a hand generator which prepares the valve circuits. The invention is described as applied to a party-line system in which parties are called by an auxiliary generator connected to the repeater circuit. The parties may be connected to the exchange over a single-wire earth-return circuit or over a two-wire line. Call to main exchange, single-wire system. The subscriber A1 operates his hand generator 9 and an alternating current train energizes the A.C. relay 22. Relay 23 pulls up, preparing a circuit for 25, completing the filament circuit for the valves 34, 35 and starting the 1000 cycle oscillator OS. When the calling signal terminates 25 pulls up and 24 operates. Relay 23 falls away, completing the circuit to the plates of the valves and breaking the original filament circuit, but this circuit is maintained by 24. Relay 25 de-energizes but its armature vibrates to hold 24 until earth is returned over 51. The calling subscriber removes his receiver whereupon the voltage of the local transmitter battery 4 is impressed on the grid of valve 34 to give a positive impulse to valve 35. Relay 26 pulls up and is held energized by the normal high tension supply. A loop circuit is thus completed over 50, 52 to the line switch LS which hunts for a free selector S and the release relay in S (not shown) earths the conductor 51 to hold 24, 27, which energized in the loop circuit over 50, 52. The subscriber manipulates the dial CD in accordance with the digits of the wanted number. On the first break, the local battery potential is removed from the grid of the valve 34 and a negative pulse is repeated to 35 which lowers the current flow through 26. Relay 26 falls away breaking the loop 50, 52. When the dial springs remake at the end of the first impulse, the local battery potential is again applied to 34, a positive pulse is transmitted to 35 and 26 re-operates This cycle of operations is repeated for each impulse of the digits which set the selector S and connector C1. The code ringing selector CS is set by the last impulse train to select a code conductor over which relay 307 is controlled to apply suitable ringing from generator G2. to the wanted line. The call is completed in the usual way. When the calling party clears, the local battery is removed from the valve 34 so that 26 again de-energizes. As 26 remains' back, relays 302, 303 in the connector release; earth is removed from 51 and 24, 27 fall away to restore the apparatus to its normal position. The 1000-cycle current fed from the oscillator OS over transformer 46 to the grid of valve 35 makes the operation of 26 more reliable. The valve 35 may be dispensed with, the relay 26 being placed in the plate circuit of valve 34 in place of the resistance 44. Call to single wire party. If a call is to be extended to party A1, the leads 50<1>, 511, 521 are selected by the connector 01 and relay 28 operates. When relay 307 responds to the code generator, ringing is supplied to lead 521, and is without effect, but the earth connected to lead 50<1> energizes 21 which supplies suitable ringing from G1 to the line 10. Relay 25 operates each time 21 pulls up and energizes 24 which completes the valve circuits so that relay 26 is energized when A1 replies. Relay 27 pulls up and 28, 21 fall away to complete the speaking circuit. Call to another patty on same line 10. To call a party on the same line, the subscriber A1 operates his generator 9 to send out the appropriate code. Relay 22 responds as before to energize 23, and relays 24, 25 pull up on the termination of the first pulse. Relay 22 also responds to succeeding pulses and opens the plate circuit to the valve to prevent 26 following the reversals of current impressed on the line and setting a switch train. When the subscriber A1 removes his receiver, relay 26 energizes to seize a line switch and a selector from which guarding earth is applied to 51 to guard the line against incoming calls. Two-wire line system. If two wires are provided to the party Al, the line 3 is connected to point 32 instead of the two points being joined to earth. To enable the potential of the local transmitter battery to be impressed on the grid of the valve 34 under these conditions, the terminal 33 of the repeater is connected to earth.