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Re: frequency (fwd)



Tesla List wrote:

>         The answer to your question is no.  Creating a current source of the
> right frequence to resonate with the secondary is the job of the primary
> coil and capacitor.  The transformer's job is to supply power to the
> capacitor.  The spark gap performs a special function in the tesla coil
> tank circuit.

Actually, it is possible to supply the primary coil with current at the
right
frequency and use the transformer resonance to amplify the input voltage
by more than the square root of the inductance ratio alone would. This
is 
usually done with an oscillator made with a high power RF tube. A "tube 
coil", as usually mentioned. 

> In order for the primary
> to produce a rapidly changing magnetic field, it must have a sudden rush
> of current through it.
>         The spark gap's job in all this is to help provide that sudden
rush of
> current.  As the capacitor charges from the AC source, the voltage across
> the spark gap increases.  Eventually, the voltage across the spark gap is
> so much that it arcs.  When it arcs, all of the charge on the capacitor
> rushes through the primary coil. 

More exactly: When the gap fires, the current starts to oscillate back
and
forth in the primary tank, and as the secondary resonates at the same
frequency of the primary, the oscillation is gradually transferred to
the secondary (voltage and current oscillations in the secondary rise 
with a sinusoidal envelope, while voltage and current in the primary 
decrease with a cosinusoidal envelope, if the losses are low). When 
the average current through the gap decreases to a value that is not 
enough to keep the arc conducting, it ceases to conduct ("quenches"),
and the energy is "trapped" in RF oscillation in the secondary, until
entirely dissipated. The maximum output voltage is never higher than
the gap breakdown voltage times the square root of the inductance
ratio.

Antonio Carlos M. de Queiroz