# Re: Harmonics

```Hello Cabbott, all,

You wrote:

SNIP

.... this is akin to pushing a swing every time it rocks back.

SNIP

This WAS how I thought a Tesla coil worked a while ago, too. However, new
discusions and thoughts have lead me to believe this is NOT how a spark gap
driven Tesla coil works.  I guess you are talking about someone sitting on a
swing and a second person gives the swing a push (with the equal amounts of
energy each time) each time it comes back to the "pusher". This will let the
swing rise higher and higher after each push. Analog to this, a coil would
experience a voltage rise, which would continue to climb up and up (voltage
wise). What you are talking about is resonant rise. A spark driven Tesla coil
does not experience resonant rise. A Tesla coil should be viewed more like a
lightly coupled transformer.

You store an "x" amount of energy in the primary cap. When the gap fires this
energy is transferred to the primary coil. The magnetic field generated by
this surge induces a voltage across the secondary (inductive energy transfer).
Not all of the primary energy is transfered into the secondary during one
oszillation, so you want the tank circuit to be able to "swing" a few times
(more on that in a minute), before the gap stops conducting. This is the
maximum amount of energy you are able to store in the secondary. Now you can
transfer this energy into something usefull (like making sparks).

A toroid sitting on top (capacitor) of the coil stores the charge and will
prevent the voltage from breaking out immediately. The bigger the toroid, the
higher the voltage it can store, and the longer it takes for the charge to be
stored because your coil cannot deliver the voltage needed for a full charge
in one cycle. This means the coil will not arc after every bang. If you have
an excessively large toroid, you will never achive an arc, because you canīt
charge it high enough for breakout to occur. So, for hottest and longest
sparks, you will want a toroid which will promote breakout at about 70-90% of
the highest voltage your coil can make.

You want the spark gap to stop conducting exactly at the point where all
energy stored in the primary has been transfered to the secondary. This is the
way I understand first notch quenching. Letting the gap conduct any longer
will force the secondary to return some of its stored energy back into the
primary, which means losses and therefore a shorter spark.

I think a better picture of a spark gap driven Tesla coil would be a hammer
and a bell. Your hammer is the primary circuit and the bell is your secondary
coil. The bigger the hammer, the "harder" the bell rings, which is one reason
why I like using a big cap and high RF currents as opposed to a high voltage
and a small cap. This, of course, also has to do with the fact, that I am
stuck with 7.5kV NSTs (at least 6 of them in parallel can deliever 600mA) at
the time. The problem with the low voltage / high current are the higher
losses involved (IxIxR), so it might be a win or lose situation in the end.

The spark gap driven TC is not being continuesly fed with RF. Rather, a gap
driven TC is a pulsed device. A CW (e.g.:tube driven) coil might be able to
experience a resonance rise, although I am not quite sure of this, either.

A tube coil and a small magnifier (I will have to investigate what make a
maggy tick) are on my long list of "still to do" things. Before I do this,
however, I want to get my 8" coil shaped up. Considering that I am (during a
testing phase) only dumping 0.22J into it and using almost no topload (maybe
1-3pf at most) to store the charge, I think my present spark length (long way
to maximum, of course) of 20" is okay.