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Re: Pulse Transformer

Original poster: "Paul Nicholson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>

Malcolm wrote:

> Just reading all the things said in this series of posts makes me 
> wonder whether anyone, apart from myself, has trouble agreeing with
> a lot of the concepts expressed here?

> For example, since when has a TC been a wideband transformer? Since
> when did a disruptive TC not ring up with some sinusoidal waveform 
> while its primary rang down?

Yes, I agree with you on that Malcolm.

Robert Heidlebaugh wrote:

> What makes the TC differ is the fact that a sign wave is not what
> is used. The power pulse comes from the sudden discharge of a
> capacitor pulsing the primary with max voltage and hundreds
> of amps.

I've explained before that the primary waveform is sinusoidal, not
a sharp pulse.[*] 

> This pulse has a basic frequency and multiple odd harmonics
> starting at the ppf frequency

Incorrect.  There are two sinusoids of roughly equal amplitude, 
at frequencies either side of the secondary's resonant frequency.
Other frequencies do exist alongside - overtones of the secondary,
etc, but hopefully these are of negligible amplitude.

> The TC transformer is designed to pass this wide range of
> frequencies. 

Hmm, wrong.  

> The VTTC tends to be of one sign wave frequency so its output is
> by nature limited to the turns ratio of the coil.

Turns ratio - no.  It is limited by the Q factor and energy storage
capacitance of the secondary.

Xyme3-at-aol-dot-com wrote:

> I do not know if i have a clear understanding of the coil

Apparently you're not the only one.

[*] OK, there can be a sharp pulse, as the stray capacitances of the
primary are suddenly discharged through the gap.  See for example


showing Thor's base current (courtesy of Marco Denicolai). 
Immediately after firing we see quite a strong burst of high
frequency ringing finding it's way through to the secondary. Peaking
at around 10 amps, it's enough to put a few extra 10's of kV across
the bottom 10cm of the secondary.  

But these are spurious resonances which we don't exploit and have
no wish to encourage.  As you can see from Thor's waveforms, and
some examples in 


the traditional Tesla coil has sinusoidal waveforms.

The spark-driven Tesla coil exploits a property common to all pairs
of coupled resonators - coils or pendulums or gravity wave bar
detectors, whatever.  That is: when suitably tuned, all the energy of
the coupled system transfers back and forth between one resonator and
the other.  This can be very useful  - if you give the two
resonators different properties.

For example, how do you tell if a 5 ton block of aluminium is
vibrating by a tiny fraction of the thickness of an atom?  Just
mechanically couple it to a smaller, lighter object which you
arrange to have the same resonant frequency as the big block.
Along comes a tiny gravity wave, the big block hardly moves, but
after a short time, all the gravity wave energy picked up by the
huge block has transferred to the little resonator, and the little
block's movement is big enough to detect.

In the TC, one resonator is a low voltage tuned circuit (the primary)
and the other is a high voltage tuned circuit (secondary).  They
are usually coupled by sharing a little of each other's magnetic
field (the coupling coefficient, or k-factor, around 10%).  We set
the low voltage resonator ringing with some amount of energy - the
bang energy, and a little while later it has all found its way to the
high voltage resonator.  The extent to which the two resonators are
coupled doesn't affect how much energy is transferred - it all gets
across (less the inevitable losses in practice), the coupling just
determines the time taken for the energy to transfer. 

The VTTC works differently.  How can a small child lift a big fat
adult 6 feet into the air?  Just put the adult on a swing and let the
child give a suitably timed nudge at each swing.  The adult
swings back and forth, gaining a little energy each cycle from the
'input' and gradually builds up a huge oscillation over a period of
time. Here the swing is acting as a fairly long-term energy store, so
we want a leak-proof resonator, which in electrical terms mean a coil
with a high Q-factor.

You'll hear of SSTCs, which are just a Solid State version of the
Vacuum Tube TC,

As you can see, both traditional and VT/SS TCs exploit the properties
of resonant circuits, with sinusoidal waveforms.

By contrast a wideband or pulse transformer will be quite tightly
coupled, and heavily damped to kill off any resonances that would
otherwise upset the pulse shape or color the signal.  Here, the 
voltage step-up, if any, is largely determined by (and limited by)
turns ratio, whereas with coupled resonators the transformation ratio
is determined by how the stored energy accomodates itself in each
resonator - eg a tiny movement of a 5 ton block transforms to a
much larger movement of a few grams object, or four joules of energy
oscillates at 15 kV in a 15nF primary capacitor, and 600kV in a 20pF
secondary capacitance.

Well, hope that helps!
Paul Nicholson