Re: A SSTC Ground ?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Steven Ward" <srward16-at-hotmail-dot-com> 

Hi Finn,

some comments within:


>I don`t yet make any conclusions of this, other than it is possible to
>make measurements, that it is useful.
>I know that Stephen (hi!) has made great results with the same circuit,
>so it can be tweaked into working, probably by adjusting distance from
>coil and antenna length.

At one point i had the twin coils working off of a breadboard, i made no 
measurements of any kind.  Then, i built a PCB for it and checked this 
exact same thing you did, the phasing between the driver and the 
coil.  Indeed i saw a huge phase shift!  I was freaked and thought surely 
something was wrong here!  So scared that i scraped the poorly made PCB and 
put it on some perf board.  Again, the same phase shift (and it looked to 
bo 60 degrees or so).  With a teslathon the next day i figured, i may as 
well see what happens.  I cranked her up to 120vAC input, and it flawlessly 
produced bright 34" sparks!  The heating was not a problem which suggests 
to me that the fact that it does not *appear* to be ZVS may not really be a 
problem.  I cant explain it at all, but that phase shift has stayed with me 
since the start and has never caused any trouble.

>But without measurements?

As i mentioned, i had the coil working without any measurements 
really.  The only thing i always test is for either the tuning if im 
running a free running osc, or that feedback is taking over if running a 
feedback system.
I usually get feedback to kick over at some 4vAC input.

>I would like to stick a cap in the ground lead and derive the sync.
>signal from there, as suggested by mr. Herrick, and it is the problems
>associated with the ground lead that prompted this thread. I would like
>to see that signal on the scope first, before piping it into the
>comparator.

Just make sure your clamping diodes (whether they be germanium or signal 
diodes) are in good shape!


Also, consider a current transformer as a means of feedback.  Ive tried but 
was never successful.  Basically use one of your gate driver transformer 
type ferrites and wind some 30-60 turns of wire on it (you will need to 
experiment) and pass the ground wire of the coil through the toroid.  Now, 
on the output, you need diodes to clamp the voltage to a safe level.
Usually, we use 2 sets of signal diodes.  Put 2 diodes in series across the 
output of the transformer, and then put another set going in the oppisite 
direction.  This clamps the voltage to whatever the forward voltage of the 
diode is (i think i ended up with a 1.7V squarish wave after the diodes 
were there.  Then find means of feeding this into the comparator via a 
capacitor to keep it strictly AC.  Ive heard of others having some success 
with this using filtered DC as the supply, but with half-rectification the 
arcs to ground get thin and bad sounding (from something going wrong with 
the comparator).  Good luck anyhow, its something to think about.

Steve Ward


>However, I`l probably try to see it on a cheap analog scope at low
>power.
>
>There is a construction picture of the h-bridge with it`s piggyback
>driver here:
>
>http://home5.inet.tele.dk/f-hammer/Resize-of-sstc1.jpg
>
>With 2 AMD K6 coolers it runs wonderfully. The gate resistors are not in
>place on the pic.
>
>This is fun
>
>Cheers, Finn Hammer

_