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They are a basic vibrator coil. Power pulls the armature that manipulates the diaphragm til it contacts the points insulated actuator tab and breaks the circuit then it rapidly moves to continue the process. This creates a vibrating oscillation that makes rapidly moving diaphragm emit the tone. The armatures have a set air gap (different set ups may have different air gaps). The diaphragm generally has a tension adjustment to get the smoothest tone. A person has to play with that some to see how it acts but keep in mid that it was originally preset so adjustment is usually not necessary. Points can get crusty over time and would need a clean up. If the coil is still good (has continuity with an ohms reading) then it should still work as long as the points and armature are still working properly. The diaphragms can crack so a person should inspect them too.