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

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

> 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. RQ

 DF> The caps are DC rated at 25,000 Volts....
 DF> - The caps were made about 1965, so are at least 30 years old. 
 DF> - They are filled with a very high quality mineral oil (the 
 DF> meaning of the "Vitamin Q" designation). The oil includes 
 DF> stabilents and moisture scavenger materials. Absolutely NO 
 DF> PCBs are in this stuff. That's a real relief, given the glass 
 DF> envelope.  The oil is still in use today.

 DF> - The units use an impregnated craft paper dielectric and are 
 DF> made up internally of two or more series connected sections.

 DF> - Internal inductance is low, on the order of .5 microH. 
 DF> - He cautioned against wiring the units in parallel. A failure 
 DF> in one will cause the energy in its mates to dump into the 
 DF> failure point. - He felt that the units would hold up in the 
 DF> given application but cautioned to use a shield for protection.  
 DF> He has seen dielectric failures near the glass surface shatter 
 DF> the envelope.

OK, I am pretty sure from this additional information that you have
provived that I have heard about these type capacitors before and 
was advised by Bill Wysock (of Tesla Technologies) that they are a 
potential explosion and fire hazard when used in the Tesla Tank 

 DF> - The units were designed for use as RF bypass caps on
 DF> high- power transmitters.

Which matches the description given by Bill Wysock who had one
explode in his living room while demonstrating a coil. The 
description he gave of flying shards of glass and smoking hot 
mineral oil did not sound too pleasant.

 DF> Given this information, I think that I will relegate these to
 DF> use as bypass caps in the protective circuits, and go with a
 DF> homemade rolled polyethylene cap or a surplus commercial unit. 
 DF> I'll check a few of the Chicago-based sources that you
 DF> mentioned. 

Sounds good to me!

 >  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. RQ 

 DF> See above...
If I recall correctly you have four of these caps. Placing all
four in series would give you about .003 uF which is still too
much capacitance for bypassing on a neon.

 >  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. RQ

 DF> I'll go with the series design in the GIF.  Is this OK with a 
 DF> 15KV neon, or do I need two units?  Can I increase the gap on 
 DF> a single unit to work at 15KV with a single series gap unit?

A single unit will work fine, just be flexible in your design and
try to accomodate a longer electrode, or even use 8 inch PVC drain
pipe (instead of 6 inch pipe) for the gap housing and use a 7 1/2
inch, high CFM, cooling fan with some 1-1/2,  2,  or 2-1/2 inch 
diameter hard copper pipe electrodes. Or, you could use smaller 
electrodes and add more gaps; by tapping in the middle of a bank 
of say, 14 electrodes, you can run two identical parallel gap paths 
in a single unit.

I hit my first solid five foot spark with ONE of these gap units in
the tank circuit. It was heavily loaded, and it got plenty hot after 
running two minutes, but it make the sparks... This is a good design
or I would not have taken time to diagram it on a GIF file.
 DF> By the way, the address for Jefferson Electric in Downers Grove 
 DF> that was given in your list of resources has changed.  They are 
 DF> now located in Elk Grove Village, Illinois - phone is (708) 806-
 DF> 6500.

I will update my file, thank you!

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