7A1 automatic exchange circuit diagram

Inventory number: T99 1/11/2
Year of creation: 1928
Location: Hall 1

When the subscriber lifts the handset, his/her line is connected to the direct-current source of the exchange, and the first call finders (I. Hk) are activated. If one of them finds the calling party's line on the contacts of the arc, there it stops and lets also stop the other rotary call finders. It lets however rotate the second call finder (II. Hk), which looks for the first call finder positioned on the subscriber's line. Then the register finder (Rk) starts to rotate, which switches the line through the connecting circuit to a free register . The register signals by the dial tone at the subscriber that he/she can now dial the number to be called. The calling dial, by interrupting repeatedly the circuit, produces pulse trains, the number of which corresponds to the digits dialed. The register collects, i.e. registers the pulses, and according to them it controls the preselectors (Csv) and the final selectors (Vv), selecting the called line at stages according to the pulse trains.

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