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In this post here
there is a device that is cited in @paulster2's response that is called a 'vibrator'. Here's the diagram from his answer where it illustrates it.
There's an adjustment nut, contact spring and apparently a gap that's created as it 'vibrates'. Is this some sort of bi-metal strip that makes contact for a spark when electricity is run through it, like a turn signal?
My Question
What is the use of a vibrator and what does it do on old ignition coils?
AKA Trembler Coil
The trembler coil was a device called a Ruhmkorff or induction coil, widely used in the 19th century.[3] It combines two magnetic devices on the same iron-cored solenoid. The first is a transformer, used to transform low voltage electricity to a high voltage, suitable for an engine's spark plug. Two coils of wire are wound around an iron core. The primary winding carries the low voltage battery current, and the secondary winding generates the high voltage for the spark plug. Attached to the end of the coil is an interrupter or trembler, a magnetically operated switch or relay, which repeatedly breaks the primary current to create flux (changes) in the transformer needed to produce high voltage.
The switch contacts are on a springy iron arm, which holds them closed. The arm is mounted near the iron core. When battery power is applied, the coil acts as an electromagnet; the magnetic field from the core pulls the iron arm, opening the switch contacts, interrupting the primary current. The magnetic field of the core is switched off, allowing the arm to spring back, closing the contacts again. Then the primary current is turned on again, and the magnetic field opens the contacts again. This cycle repeats many times per second, while power is applied to the coil. A similar mechanism is used in the electric bell.
As the circuit opens each time, the energy stored in the solenoid's magnetic field is released and by electromagnetic induction produces a pulse of high voltage in the secondary coil winding. This voltage is sufficient to fire a spark plug located in the engine's cylinder, igniting the petrol mixture.1
The difference between a trembler coil and a modern ignition coil is that in a modern coil the primary current is broken only once by the contact breaker for each cycle of the piston, creating a single spark. In the trembler coil, in contrast, each "break" of the trembler contact produces a pulse of high voltage from the coil. During the time the points in the timer are closed, the vibrating trembler arm produces a series of high voltage pulses, producing multiple sparks.
This is where MSD got the idea for Multiple Spark Discharge, only they use electronics and modern capacitors to get the job done.
