Re: SSTC theory (scope shots)

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Original poster: "Malcolm Watts" <m.j.watts-at-massey.ac.nz> 

Hi Steve,
           Thanks for posting this:

On 30 Jun 2004, at 17:55, Tesla list wrote:

 > Original poster: "Steven Ward" <srward16-at-hotmail-dot-com>
 >
 > HI,
 >
 > Ive been trying to follow along here though my electronics training
 > (none) sort of hinders things.
 >
 > Anyway, thought some of you may be interested in some tests i did with
 > my original ISSTC.  I decided it was time to try primary current
 > feedback to drive the coil.  So how i went about it was put an 90:1 CT
 > (home made) on the output of my H-bridge driver.  The CTs output
 > drives yet another CT (60:1) to basically reduce the current on the
 > output... mainly so i dont overload my driver board with a lowZ
 > feedback source.  Anyway, it works.
 >
 > A pic of the setup:
 >
 > http://www.hot-streamer-dot-com/srward16/ISSTC/2004_06_29/100_0068.JPG
 >
 > I took some pics with various tunings, but it seems my original tuning
 > (used with secondary base feedback) works the best.  The following is
 > the RF output from the secondary coil:
 >
 > http://www.hot-streamer-dot-com/srward16/ISSTC/2004_06_29/100_0067.JPG
 >
 > This is PRE-BREAKOUT.  You can see that im turning the bridge off at
 > about 7.5 divisions in that picture.
 >
 > Here is what happens when i start to get breakout:
 >
 > http://www.hot-streamer-dot-com/srward16/ISSTC/2004_06_29/100_0066.JPG
 >
 > Notice that the later half of the envelope looks distorted... i think
 > this correlates with when breakout is achieved (i can reduce the burst
 > length to that point and still hear just a slight crackling).  So
 > indeed the ISSTC system relys on driving lots of *CW-like* power into
 > each spark.  As i turned it up more, it appeared to breakout after
 > just 6 cycles.  Also, i can keep adding cycles to lengthen the sparks,
 > while this is obvious, it seems that this effect was more pronounced
 > with primary feedback than with secondary feedback (but i may need to
 > test this again).

In some respects this is really disappointing because it means that
current is ramping up in the primary as well as the secondary does it
not? If so, it looks like there is no escape from scaling the power
supply component capabilities to match an increasing power output (in
which case who cares about feeding an established streamer CW). I had
thought it would be possible if not likely to prevent the driver from
seeing increasing currents like this. One cannot stop a base-drive
system from seeing with peak resonator base currents although these
are typically far lower than primary currents. So it looks as if in
the double-tuned system, the artifacts of double-tuning remain
despite a constant feed of power into the primary (Y-N)?

 > Also, this is an older shot of the RF output with secondary base
 > feedback:
 >
 > http://www.hot-streamer-dot-com/srward16/ISSTC/waveforms/100_0074.JPG
 >
 > Note that its a rather linear ring up, but as you begin to really push
 > the power, it looks like the predictions in Antonios paper (fast ring
 > up and levels off for the rest of the burst).

I'd like to see what's happening in the primary circuit in that
scenario and it would be interesting to see the primary current
waveforms for the previous case also.

Malcolm