Re: New DRSSTC...new question

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Steve Ward <steve.ward@xxxxxxxxx>

Hmm, i hate to say it, but both of those capacitors seem rather small 
in my experience.  My smallest coils use .075uF, for 18" and 36" 
sparks (they operated at 350khz and 200khz respectively).  My medium 
coil uses a rather large 450nF (yes, .45uF) for 6 foot sparks at 
about 56khz.  My largest machine uses .36uF (soon to be increased to 
.45uF or .56uF) and runs around 42khz.

Designing a DRSSTC is different than a spark gap coil.  We need to 
operate at very low frequencies (because of IGBT limitations).  This 
usually means that we use a much bigger tank cap, and a typical 
primary inductance, but i go for very high coupling (.2 to .25 if 
possible).  You might note that my smallest coil runs at 350khz, i 
had to use rather over rated IGBTs for it to work properly.  Its much 
easier if you are working <100khz.  Dont be afraid to use very thin 
wire (i use 30awg on the 6 foot spark coil).  I personally dont think 
high secondary Q is completely necessary for long sparks.  With a 
DRSSTC, we keep driving the coil beyond breakout.  By the time the 
toroid breaks out, the Q is indeed quite low.

And see my website if you havent:

<http://www.stevehv.4hv.org/>http://www.stevehv.4hv.org/

Steve

On 9/19/05, Tesla list <<mailto:tesla@xxxxxxxxxx>tesla@xxxxxxxxxx> wrote:
Original poster: Skip Greiner <<mailto:sgreiner@xxxxxxxxx>sgreiner@xxxxxxxxx>

OK. The feedback toroid is now cold! Thank you all.

New question: I can use a .04mfd primary cap and 7 turns of wire or a
.02 mfd primary cap and 9 turns of wire. How does one determine the way to go?

Thanks again
Skip