Telephone bell with clapper loosely coupled to armature - has rod in slot allowing loudness adjustment but not silent working

摘要

The armature (8) of a telephone bell rocks when ringing current energises the solenoid (7). A lever (11), attached to the armature, has a pin (25) at its far end which engages in a longitudinal slot (17) in the clapper (18). The clapper lies between the two bells (2,3) and is pivoted on an eccentric (13) on the loudness control wheel (13). Turning the wheel moves the clapper towards or away from the bells and so varies the loudness of the ring. In the extreme 'silent' position, the clapper does not strike the bells at all, but there is still sound from the pole pieces (9,10). Since the armature lever is loosely coupled to the clapper by the pin and slot, there is no risk that incorrect adjustment will prevent armature movement.