Patent GB-704108-A (GB)
Title: Telephone switching systems employing gas discharge tubes
IPC: H03K17/52
Filed: 1951-12-18
Abstract: 704,108. Semi-automatic exchange systems. WESTERN ELECTRIC CO., Inc. Dec. 18, 1951 [Dec. 19, 1950], No. 29598/51. Class 40 (4) In a gas-discharge tube switching network in which the application of certain potentials to selected ones of a number of terminals at each end of the network creates a conducting path across a plurality of gas-tubes between the selected terminals, further potentials are applied to the selected terminals to maintain the whole conducting path which serves for the transmission of speech or other varying voltage signals. The network may be used to connect subscribers' lines with operator's connecting circuits which give access either to junctions or other paths through the network. The gas-discharge tubes are as described in Specification 686,427 and are operated at a negative resistance portion of their characteristic. A small semi-automatic exchange is described below. Setting up a connection from subscriber 130 to subscriber 210. The line relay 136 lights the calling lamp 139. The operator, having ascertained the caller's requirements and that the wanted line is free, selects a free connecting circuit such as that comprising tubes 360,350. She operates groups of switches or keys 270 ... 272, 470 ... 472 in accordance with the three figure numbers of the called party and one end 360 of the circuit, respectively, and throws a start key 273, 480, 473 to the connect position. Tubes such as 001, 002 ; 350, 360 individual to the subscribers' lines and the ends of the connecting circuits, respectively, are similar to those described in Specification 548,392, [Group XL]. In the called subscriber's tube 001, a discharge is initiated between the control electrodes 0014, 0015 by the tens and units digit markings and due to the hundreds digit marking the discharge transfers from the control electrode 0015 to the main electrode 0012 and finally the discharge is between the main electrodes 0011, 0012. The control electrode discharge also occurs in other line tubes having the same tens and units digits. The tube 360 fires in a similar manner to the line tube 001, so that the potentials of the terminals of the four stages of tubes corresponding to the called line and the chosen connecting circuit end are changed from Œ 255v. to Œ 305v. The links between the switch stages are connected through resistances to bus-bars, the potentials of which are altered when the start key 480 is moved to the connect position so that the first and fourth stage tubes such as 324, 411 connected between the marked terminals and free links fire. The resulting decrease in the potential across the fired tubes raises the potential of the associated links so that second stage tubes such as 426 connected between seized and free links fire and increase the potential of links to the third stage of tubes. The ignition of a third stage tube such as 413 completes the path between the marked terminals whereupon the voltage drop across the path decreases sufficiently to busy the links of the completed path and to prevent the ignition of a further third stage tube. The operator restores the start key and the digit switches. The discharges through tubes 001, 360 cease and incompleted paths through the switch stages release. In the called subscriber's line circuit relay 217 lights the busy and supervisory lamps 220,218, and the busy lamp 365 of the seized end of the connecting circuit is lit by relay 364. Similarly the operator connects the other end 350 of the connecting circuit to the caller's line whereupon the busy lamps 140, 355 are lit. The talking connection is now complete, and other connections may be set up. Unwanted surges which may occur when further connections are set up are limited by limiters such as 214, 215 connected in the line transformer circuits such as 211, and by earthed condensers 483 ... 485 connected to the bus-bars. Release.-The operator sets her digit switches to the number of one of the subscribers and throws the start key to the disconnect position. A discharge is set up in the reverse direction in the line tube 001 or 002 and the resultant lowering of the potential of the upper main electrode breaks down the speech path between the subscriber and the connecting circuit. The operator releases the path between the other subscriber and the connecting circuit in a similar manner. Alternatively she may release the connection using switches 470 ... 472 to cause reversed discharges in the connecting circuit tubes 350, 360. Specification 664,526, [Group. XL (a)]. also is referred to.