CLOCK No. 17

MECHANICAL CLOCKS
Clock No. 17A - Description

1. General
Clocks No. l7A are used with associated apparatus (see Dgm. AT 2041) to give half-hourly audible warnings in telephone exchange switch rooms of nine or more working positions during traffic call-counts.  In new exchanges fitted with master clocks (Clocks No. 36) Clocks No. 62A are used in place of Clocks No. 17A (see B 1342).

2. Description of clock
Clock No. l7A is an 8 day mechanical lever-movement, housed in a rectangular mahogany case.  The movement is wound from the front, and the winding key is kept inside the case.  The clock is provided with a small circular dial divided into 60 divisions and has only one hand.

3. Description of movement
The movement consists of two spring-driven time trains.  The first is a lever and escapement-controlled train, driving the single hand H.  The second, which has no escapement, drives cam D which operates contacts C.
Cam A, attached to the axle of hand H, operates the lever arms B and BB at half-hourly intervals, when the hand is in the position equivalent to 6 and 12 o’clock.  The operation of the levers B and BB releases the time trains associated with the cam D, which in turn operates contacts C. The contacts C close, and complete the bell circuit for approximately 3 seconds.

Last revised: June 18, 2017