Improvements in or relating to automatic telephone exchange systems

741,545. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd. Jan. 15, 1953 [Jan. 26, 1952], No. 2191/52. Class 40 (4). In a system employing cross-bar switches for completing connections between subscribers' lines in which common equipment is provided for controlling the operation of the cross-bar switch magnets, eachof the switch magnets is individually associated with a gas discharge tube controlled from the common equipment, the arrangement being such that the common equipment is enabled to release upon the striking of the appropriate gas discharge tubes and before the operation of the switch magnets. Each switching stage consists of primary and secondary cross-bar switches connected by link circuits and a connection is set up through a stage by marking all available paths extending from a primary switch through the secondary switches, selecting one of these available paths, and by causing the operation of the switch magnets appropriate to that path due to current flow through the associated gas discharge tubes; the marking of the paths, the selection of the one path, and the operation of the magnets being effected under the control of the common equipment common to the whole or part of the stage. General operation, Fig. 1. A subscriber's line passes through the MDF and IDF in the normal manner to the exchange equipment SLC individual to its line circuit. The switches of the combined line-finder and final selector LF/FS are controlled by a line-finder/final selector common control circuit LFCC. Outgoing calls are extended to a group selector GS through a trunk relay set TRS, which also gives access to a register REG via a register connector RC, and the register is associated with a common control circuit GSCC for the group selection stage by a connecting circuit CCC. Incoming and outgoing relay sets IRS and ORS respectively connect the group selector GS to junctions EJ to other exchanges. On the initiation of a call, the appropriate line-finder/ final selector common control circuit is seized, sets up a free path through a line-finder/final selector unit electronically, and is, immediately released. This operation is completed in 2-3 milliseconds by striking cold cathode discharge tubes associated with individual select and bridge magnets of cross-bar switches, the tubes being maintained conducting to operate the switch magnets after the common control circuit has been released. A trunk relay set is seized by the line-finder/final selec