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Re: Character Revisited
Hi all,
I would like to make a few comments on this piece....
> R. Hull recently posted an excellent post comparing the character of TC
> discharge arcs with different drivers.
from RWW......
> As a follow up, I forward a portion of a post from a nonlist member.
>
> I had ment to make clear, that if you could drive a TC with a
> class A solid state, or vacume tube driver, and a signal with the
> same frequancy components as a spark gap, you would see the same
> arc lenghts per primary power levels as you would get with a gap.
I think it's important to recognize that the duty cycle of a gap
(a few percent if that) is vastly different from that of an oscillator
(100%). An oscillator produces a power arc with a continuous high
degree of channel ionization whereas the gap system produces distinct
discharges with only some maintenance of ionization and that
discontinuity allows the discharge terminal to reach a much higher
peak voltage for each bang. The secondary Q is not constantly low for
a cap discharge system but varies between unloaded (no power through
between gap fires) and heavily loaded several cycles after gap fire.
> I think it's not the gap, but the frequancy content that makes
> gaps appear to deliver longer secondary arcs for a given power
> level. Unless the frequancy components of the primary current are
> the same for the tube or transistor driver, we cannot make diurect
> comparisons to gap driven coils.
They never will be identical IMO because of the continuity vs
discontinuity. Was the arbitrary waveform generator maintaining the
normal gap-type duty cycle or simply putting out the waveform
repetitiously?
> I've used some fancy soild state drivers with the same coils that
> have been driven with gaps, and while I cannot claim to have
> proven this exaustivly, it seems that gap vs. tube or transistor
> makes no differance. A clean primary current (spectrally pure
> that is) is less 'efficient' (as measured by secondary arc lenght)
> than the mess from a gap.
Same as above. Actually, the gap is not totally bad in this regard
either. There is a side-frequency generation for a pure unloaded
ringdown in a cap discharge primary and there should be - its
amplitude is changing wrt time.
> To do this, I digitized an actual gap with a HP arbitrary waveform
> recorder/generator, and fed this through Phase Linear DC to 100
> Khz amplifiers. A RF wattmeter was used to adjust the gain of the
> Phase Linear amps (two bridged together) so that the primary
> current was as close to that measured (by the same watt meter)
> when the coil was driven with the gap.
Question - was the low duty cycle of the gap discharge maintained?
This is very important. Note also that at those low energy levels
voltage production in a disruptive system is approaching that of
comensurate spark length (in my experience).
> Guess what, same arc lenght. Alter the frequancy components of
> the waveform, and the arc lenght appears to change at a faster
> rate than when the power levels alone are changed. So I agree
> that the arc is important, but why the arc is important may have
> more to do with the frequancy profile of the primary current than
> it depends on what kind of driver is used.
>
> I claim that if you deliver the same primary current waveform with
> a tube or transistor as is delivered with a gap, you get identical
> performance with each driver.
>
> snip . . .
>
> Getting back to the gap vs. tube or transistor discussion, in my
> mind it all boils down to what is inside the wave, it's internal
> structure and frequancy/phase profiles. If we extend frequancy
> and phase to the pure potnetial waves, then scalar and EM really
> are the same things.
>
>
> Has anyone run a spectral analysis on a spark gap discharge? It may be
> informative to alter the spectrum or perhaps delete or add spectral
> components in order to enhance TC preformance. Take heart Alan Sharpe.
Be interested to hear other's views on this.
Malcolm