* Original msg to: Froula-at-cig.mot-dot-com

 DF> From: Don Froula <froula-at-cig.mot-dot-com>
 DF> To: richard.quick-at-slug.st-louis.mo.us

 DF> Richard, I've had a few days to review your tape.  Besides 
 DF> being blown away by the sparks (!), I'm really impressed at 
 DF> how you've taken a very methodical approach to increasing 
 DF> your coil performance. It certainly has paid off in results.

Thank you very much.

 DF> Actually seeing the materials and construction methods 
 DF> involved is really a great help to my own little project.  

That was one of the reasons I put the material on tape. The proof
is in the blowout spark discharges.  

 DF> I have a few specific questions.  I'm planning on building a 
 DF> 6" coil, 24" winding length wound with 22 ga. enamelled magnet 
 DF> wire. I was planning on using 60' of 3/8" copper tubing for the 
 DF> primary.  I am tentatively planning on a single 15,000 V, 60ma. 
 DF> neon transformer to power it, using a balanced circuit like in 
 DF> your big coil.  Each leg of the circuit will use two .012 uF, 
 DF> 25,000 V. oil filled commercial capacitors in parallel.  This 
 DF> should provide .012 uf of tank capacitance at a DC voltage 
 DF> rating of 50,000 volts. - Is the rating on the commercial caps 
 DF> conservative enough for the 15KV transformer?  I could step down 
 DF> to a 10 or 12 KV unit. 

Is the commercial cap DC or pulse AC rated? That is the question.
Wired as you stated, they should hold up even if they are DC rated,
but even my big pulse rated caps came without any warrantee :-)
The next question is... Even if they are DC rated and they hold up,
will they give the best performance? My experimentation shows that 
a well designed homemade capacitor will blow away most "surplus"
caps that have the voltage rating. Most surplus caps, especially
with a DC rating, are not designed to pulse. 

 DF> - Is there any real performance advantage to winding the
 DF> primary in a saucer rather than a pancake configuration? 

Primary design is dependant upon the aspect ratio of the secondary.
Smaller diameter secondary coils with aspect ratios over 3.5 work 
best with saucer primaries. As the aspect ratio of the secondary
coil comes down to 3, then the primary needs to flatten out to the 
pankcake type coil to keep from overdriving the high inductance
secondary. In general, a six inch diameter secondary needs a saucer 
shaped primary, an eight inch diameter secondary (and larger) works 
best with a flat pancake type coil. This assumes you are using a 
good high Q capacitor.

 DF> - I was planning on eliminating the bypass caps on the filter
 DF> circuit, using only a protective gap and chokes for tank 
 DF> circuit isolation (along with a line filter on the neon 
 DF> primary).  Is this adequate protection for the transformer 
 DF> in a circuit like this?

Not with Tesla's balanced circuit. This particular circuit is the
worst when it comes to RF kickback, and is hardest on the neon.
You will have to have bypass capacitors if you use the balanced
circuit. If you put the spark gap in series with the primary, you
can get away, maybe, without bypass caps. 

 DF> - You mentioned excessive kickback unless the capacitive
 DF> values of the two tank legs were carefully balanced. 
 DF> How important is this in a coil of this power level?

How important are your neons at this power level? 

 DF> - I was planning on using your "air blast" single quenched gap
 DF> design from the GIF.  Will this supply reasonable performance 
 DF> for this coil?  How about using a high-power vacuum cleaner 
 DF> blower fo quenching?

Compressed air gaps give wicked, wicked, performance. Unbeatable
with neons, and they work with heavier xfmrs as well. But they
have drawbacks: noise, compressor requirements, and dielectric
stress on the capacitors. Wicked performance in the gap puts great 
demands on the capacitor. The cylinder series static gap, assembled
with seven parallel electrodes spaced at about .028 -.030 inches
will work well, and does not have the drawbacks of the compressed
air quench gap. The cylinder series static gap in the video (the
one that did not quench well) was designed as a single component 
in a sophisticated gap SYSTEM; the system had about a dozen static 
gaps, plus a rotary, and worked extremely well. A single cylinder
static gap designed to work alone is quite serviceable in these
powers levels and give good, solid, reliable, cheap, performance.
Vacuum gaps are also excellent performers, but they are a bit
harder to engineer. 

 DK> - Any suggestions on spacer construction for the primary?

I cut strips of plexi, then cut spaced slots for the primary 
conductor. The plexi strips can be glued to wedges of plastic 
to construct saucer type primary coils

 DK> - How important is the variac for tuning a coil of this size? 
 DK> I have a 7500 V, 30 ma unit I could use for lower power
 DK> tuning.  Can I get by without?

Trust me. I ALWAYS use a variac, a good ground, and a line filter.

 DK> - I found some 18" outside diameter, 2" cross section styrofoam 
 DK> toroid forms in a local craft store.  I was planning on covering 
 DK> this with aluminum tape and adding an aluminized disk center 
 DK> support.  I calculate a surface area of just over 100 square 
 DK> inches for this terminal.  Is it adequate, or would I do better
 DK> with the 4" drain pipe version. 

The toroid you describe is fine. It may breakdown at a slightly lower
voltage than a toroid discharger with a 4" cross section, but that 
would not stop me from building it. When I go to experiment with coils, 
I have never have enough sizes, shapes, and numbers of toroids.

Richard Quick

... If all else fails... Throw another megavolt across it!
___ Blue Wave/QWK v2.12