Re: Certain s.s. phenomena; to J.F. et al

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

Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" <FutureT-at-aol-dot-com>

>>>      [  snipped thoughout.......  ]
>  > But in a tube
>  > CW coil, with constant drive with changing impedances, and the
>  > peculularities of the system, seems to demand a point on the
>  > toroid for the longest spark:
>  > 
>  > If I tune my coil for breakout from a toroid, then I get short 
>  > sparks. If I tune for longest sparks from a point on top of the toroid, 
then 
>  > the coil cannot break out without the point.  
>   
>  ...So clearly, the attainable voltage has been reduced.

Ken, all

Yes, I believe the voltage has been reduced, although the
primary tank is tuned to a similar frequency to the secondary.

By the word mis-tuned, I mean de-tuned.  I deliberately tune the pri tank
to a different (higher) frequency than the secondary resonant 
frequency.  The secondary Fo = 363kHz or so.  I tune the primary to
400 kHz (calc'd), for longest sparks with a point on the toroid.
To obtain breakout from a toroid with a slight foil bump, I have to tune
the primary to 480kHz or so.  I think the k = 0.2 or so. 

>  >  The coil has to be severely mis-tuned
>  > for operation with no breakout point, so this reduces the spark.
>   
>  With no breakout point, you must be tuned at or near a resonant peak--or, 
at
>  least, nearer to one than for the case of using the breakout point, right? 
>  Because the voltage, to get breakout from the toroid alone, must be 
higher.  

I guess I may be tuned to one of the frequencies that corresponds
to one of the double humped frequencies, more or less.  I also
suppose this gives the highest voltage before breakout.  But once
the spark breaks out, this tune point is obviously not so good, 
because the sparks are shorter than with a breakout point and the
different tune point.  
>
 >  > and this makes the tuning situation complex.
>   
>  I should say!  Mine is, I wlll say, more straightforward in that there's 
> only one resonance and I'm spot on it all the time.  But 
>  perhaps because of that I sacrifice the capability for differing
>  kinds of spark.  Have to look into that!

Yes, it should be interesting.

>  Not the secondary's circuit-impedance--I'd think its change would be the 
> same
>  regardless.  I meant the relative impedances of primary & secondary 
circuits.

Yes, that's what I was thinking you meant.
>  
>  I'd think the driving impedance of a tube-driven primary would be a whole 
> lot higher than that of the usual spark-gap primary.  My 
> MOSFET-switched primary would be somewhere in between. 
>  Although, it's pretty low all during the spark-time since it's being
> constantly driven during that time and consists
>  only of 3 untuned turns, MOSFET switches and electrolytic capacitors.

That seems reasonable.  I see what you're saying.  Yes, it is very
possible that my impedance ratio is changing more in the tube coil.
I don't know how much of what I'm seeing is due to impedance issues,
and how much to tuning issues.

>  > Duane Bylund did say that his SSTC also saw the voltage cut in
>  > half with the point.  But the ball he used was only 1" dia, and his
>  > sparks were just 7" long.  His sparks were also the same length
>  > with or without the ball I seem to remember.  Your results are
>  > interesting because they show that it is only a tube coil that
>  > demands a breakout point for longest sparks, or a coil similar
>  > to a tube coil in its characteristics.  
>   
>  Hmmm...don't know if I agree: I get much the same appearance/length of 
spark
>  from all 3 types of emitters.

That's what I'm saying; your coil is different than a tube coil, in
not having the high Z tank, nor the tuned tank.  Thus, you don't
need the break out point.  In the tube coil, I need the break out
point.  I'm not what you disagree with?
>   
>  >Your results are also
>  > interesting because they show that you don't need to build up
>  > such high voltages which perhaps stress your MOSFETS to 
>  > obtain a given spark length.  If you run with the breakout point,
>  > the impedance won't shift that much, and will shift at a lower
>  > power level.  This may permit better impedance matching, and
>  > better efficiency maybe.
>   
>  I see it a little differently:  If I run with a breakout point, I could 
> reduce the quantity of secondary turns.  Still achieving breakout, 
> I should then be able to pump more current into the spark during
>  the after-breakout period and perhaps in that way reach a longer spark.  

Perhaps.  It's not clear to me if that will actually make the spark
longer.  I just don't know enough about the spark growth requirements.
A rising envelope seems to be important, beyond that, I've never
seen much difference with different turns ratios.  Maybe I didn't
vary my turns ratios enough.  Or maybe impedance changes that
resulted in my system gave me a false impression which is very possible.
So I look forward to your results.

>  As soon as I can make up a new
>  secondary I'll check that out.  Although...I prefer to run such that I can
>  break out from the toroid if I use no breakout point.  But I have a feeling
>  that I can still reduce the secondary turns and continue breakout from the 
6"
>  x 24" toroid.

Do the sparks move around the toroid surface from place to place
as the coil runs?  They do this on a spark gap TC with a smooth toroid.

>  (All of you 10 KV people take note of that 6" x 24" smooth-toroid breakout 
>  with less than 370V applied to a 3-turn primary!  Hah!)
>   
>  >Another interesting test would be to
>  > install a much smaller toroid, maybe just 1 foot in diameter or
>  > so, instead of the 26" toroid, (sort of a corona ring), and see if
>  > this has any effect on the spark length and fatness.  Maybe it
>  > would make the spark output longer.
>   
>  Yes, but I prefer to keep the 6" x 24" in order safely to protect the 
> secondary from sparking.

My guess is that the smaller toroid would protect the secondary
just about as well.  Not too small though...  let's see.  Your coil
secondary is 1 foot in dia (?).  Maybe a 4" by 16" toroid would be very 
effective also.  Even a 3" by 15" should be good.

>    It seems the sparks are not a terrificly heavy load.
>  > 
>  > >  Marco DeNicolai had a relevant posting, on 1/31, on the subject.  
>  > 
>  > 
>  > I can't remember the posting.
>   
>  He'd made a reply to a posting of Gary Johnson, on 1/31.  Also see Bert
>  Hickman's of 2/15.  They should be archived -at- pupman-dot-com but if you don't 
> find them I could fwd them to you.

Thanks, I'll look for them.  If I can't find them, I'll let you know.
   
>  It happens that the longest sparks are at the slowest spark rates since the
>  storage capacitors' voltages don't get sucked down so much.  

I understand.  Yes, this is different than my system.

John

>  
> Ken Herrick