Quote:
Originally Posted by russell_w_b
The second set of contacts makes a spark-quench circuit by shunting the dial-pulse contacts (via a further dial contact called a 'dial off-normal' contact) with a CR circuit. This gives a clean dial pulse to signal to the exchange.
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This set of contacts also prevents the series bell capacitor being by-passed (shunted) and ensures the a.c. ringing signal is not routed to the bell partly via the receiver and the microphone, which it would do if there were only one set of contacts breaking the loop.