Adjustable Cone Vibrator.
Fig. 27 shows a form of contact breaker much used in portable medical coils for slow speeds. It consists of a cone of iron H, mounted on the vibrator spring, and furnished with adjustable contact spring and screw A. Its amplitude of vibration is limited by the two pins mounted on the disc, between which the cone vibrates. The disc is turned by hand, thus moving the pins, and so varying the travel of the cone H to and from the core C. It does not give good results from the fact that the rhythmical movements are disturbed every time the cone strikes against the pins, also at the contact spring striking the contact screw. As we showed before, a really satisfactory contact breaker should have a spring, which allows of no sinusoidal movement. Where a pivoted armature is governed by a spiral spring, the result is a series of steady, rhythmical shocks, provided the adjustments are satisfactory.
Fig. 27.
Coil Head Contact Breaker.
Fig. 28 shows the details of a contact breaker to be attached to the coil head direct. It is often used on very small coils, which, together with a miniature dry cell, is slipped into a pocket case. An important detail in small coils is to use a contact breaker of sufficient size. Most of them are not large enough to stand ordinary usage, the adjusting screw is not of sufficient diameter and the thread soon strips. There is no reason why the adjusting screw, its platinum tip, and the pillar or lug which holds it should not be solidly built, it would certainly require less adjustment. Either single or double check-nuts can be fitted to the adjustment screws of nearly all the forms of contact breakers described.
Fig. 28.