* Original msg to: Esondrmn-at-aol-dot-com

 ES> From: Esondrmn-at-aol-dot-com
 ES> To: richard.quick-at-slug-dot-org
 ES> Subject: More design questions

 ES> Richard,

 ES> I am trying to understand what value (mfd) the rolled
 ES> capacitors will be when I get them done.  I believe you said 
 ES> in earlier correspondence that they would be about .02mfd.   
 ES> I calculate about .009 mfd.  The formula should be C(pf) =   
 ES> (.224KA/d) N-1  where N = number of plates. For this         
 ES> capacitor:  K = 2  A= 1260 (aluminum 14"x90" for 4x8 sheets  
 ES> of poly)  d = .063  We probably won't achieve a true         
 ES> distance between plates of .063 (with .0625 material)        
 ES> because it probably is not practical to expect to get it     
 ES> rolled that tight. I would expect the actual value to be     
 ES> somewhat less than the calculated number of .009mfd.
 ES> Have I gone wrong somewhere? 

This time I did not make a mistake, poor though my math may be.
One of the benefits of rolled capacitors is that a two plate
rolled capacitor has TWICE the calculated capacitance of a two
plate flat capacitor. If you think about it, this makes sense.
The plates are rolled up around one another, and as far as the
capacitance is concerned, rolling has the effect of "adding" an
extra plate. When calculating for two plate rolled capacitors
either multiply the calculated capacitance by two, or, calculate
with N = 3.

 ES> I also need some education on spark gaps.  I have built one
 ES> cylindrical gap using 6.0" dia PVC pipe and 7 copper pipe    
 ES> sections of 1.5"dia and 3.0" long. I hooked this up as a     
 ES> dead short across a 12kv 60ma transformer and it seems to    
 ES> work fine.  According to the spark gap instructions, I will  
 ES> need two of these in series for 12kv at 720VA to 2.0KVA - so 
 ES> I am building another one. Some of what I have read tells
 ES> me that the spark gap is used to help tune the Tesla coil.   

Not tune as far as "frequency tune" is concerned, tune here
implies bringing the coil into "peak tune". This could still be
better stated: Simply tuning to the correct frequency does not
mean that the coil system is balanced and synergistic. A coil
performs best when it is in tune, and the system is operating 
harmoniously. To achieve harmony in a coil system that is already
tuned to the proper frequency means adjusting the toriod,
coupling, spark gaps, etc. in search of the best combination for
efficient operation. This process of "peak tuning" means lots of
time fiddling and firing with an objective eye on the coil
performance. It is part of the art.

 ES> If this is true, why do we want to use a fixed gap system?   
 ES> With two cylindrical gaps in series set at .030 each we get  
 ES> a total gap of .36 inches.  Do I really need to add a single 
 ES> fixed gap in series with all this to "tune" it?  Thanks,  Ed

Well one of the benefits of the cylinder gap is that you may tap
at any gap position, with incremental adjustments of .03 inches
per terminal. You may also run parallel paths, reducing the
current on any single gap and improving Q and quench times,
especially at higher powers. I do not think that the "single
fixed gap in series" was intended to be a fixed gap: I believe
that I was working with a rotary gap in series with two cylinder
gap units, and this gap "system" provided some of the best
performance I have ever seen. These gaps are solid performers,
they may be connected in many configurations, and are easily
incorporated into more sophisticated gap systems as the coiler
progresses. They are easy to clean and maintain, they are
portable (easy to move from coil to coil), and may be tapped for
a wide variety of total gap distances. You can't go wrong with a
couple of these gaps in your arsenal, and you will be challenged
to beat the convenience and performance.

The original brain sweat on this design was Bill Richards btw, 
I have built eight of these type gaps in various sizes and
configurations and have done a lot of experimenting with run
times, cooling efficiency, power handling, voltages, Q, etc.

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