TRAFFIC CONTROL TELEPHONE SYSTEMS Circuit - Sam Hallas

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(c) The total travel of the stepping pawl (U) shall not be less than 1¾ nor more
than two teeth of the ratchet wheel (W).
(d) The movement at the end of the stepping pawl (U) shall be such that it will
obtain full engagement with the teeth on the ratchet wheel (W) at all times.
(e) The holding pawl (Q) shall fall reliably into each tooth of the ratchet wheel
(W) as it is advanced by the stepping pawl (U) with a maximum backlash of
0.005 inch.
Holding Spring and Code Wheel
(a) When the code wheel (E) is revolved by hand the cup-shaped part of the
holding spring (K) shall clear the inside of the code pins (C) and time arm by
not less than 0.005 inch, and shall clear the lower surface of the enlarged part
of the code pins and nuts by not less than 0.015 inch.
(b) When the code wheel (E) is advanced by the armature (O) the holding spring
(K) shall clear the code pins (C) and the time arm in its outward motion by
not less than 0.005 inch.
(c) The code wheel (E) and code pins (C) shall be located so that after each
group of impulses in its own particular code the holding spring (K) shall, on
the release of the armature (O), engage with each code pin in turn so that the
pin is held in the cup and retains the code wheel in that position until advanced
by the next group of impulses or the releasing impulse. The holding
spring (K) in normal position shall press against the insulating stud on the
rocker arm (S) with a pressure of 1 gramme minimum to 3 grammes maximum.
(d) The holding spring (K) shall be adjusted to lie flat along the whole length of
the buffer and the tension against the buffer measured at the end of the buffer
shall not exceed 10 grams.
(e) Altering the Selector from 17 to 27 Step Code. To change the setting from 17
to the 27 step code, loosen slightly the two code wheel screws (F) holding the
code wheel (E) on the shaft. Step the ratchet wheel (W), by operating the
armature (O) by hand, to the 27th step and hold it. Then rotate the code
wheel on the shaft so that the contact spring makes contact with the first
ringing terminal and the permanent code pin will be in position to be engaged
by the holding spring (K). Tighten firmly the two code wheel screws (F).
Contact Spring
(a) When the selector is mounted in a horizontal position or in a vertical position
with the armature (O) at the bottom, the contact spring (Z) shall be
raised by the ringing terminals by not less than 0.02 inch when in the ringing
position.