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The size of my capacitors?



Hi everyone.  My name is Adrian Bourassa and I've only known about Tesla 
Coils for about six months.  I'm doing a science project involving a 
small coil that I saw in a fairly old issue of "Electronics 
Experimenter's Handbook."  The experiment is to duplicate the author's 
model and to try and improve on it.  
My question is as follows:
The article said to use three parallel connected 500 pF doorknob 
capacitors leading to ground, parallel to the primary of the coil.  Maybe 
there is a term for this capacitor placement that someone could fill 
me in on.  It is the final capacitor that the electricity encounters 
before it goes through the primary coil of my assembly.  I believe that 
it is used to generate the high frequency that is characteristic of  
Tesla coils.  Anyway, back a couple of months ago I had never heard of a 
doorknob capacitor (maybe you haven't either) and neither did anyone that 
I spoke to about it.  So I used the only thing that I thought would work. 
 The only 500 pF capacitors that were rated high enough voltage that I 
could find turned out to be very small.  They're a little bit fat for 
disc capacitors but I believe that is what they are.  They're only about 
a 1/2inch in diameter.  They seem to work fine.  My question is am I 
correct in assuming that if it's the right capacitance and it's rated 
high enough voltage that it will work?  The reason I'm doubtful is that 
the author gave me directions to make a capacitor if I couldn't find one 
and it's supposed to be around a 9" picture frame.  Has the technology 
improved since 1990 enough to allow this drastic a change in capacitor 
size or would I find a drastic improvement in arcing distance if I used 
the correct physical sized capacitors? 

Sorry about the lack of correct terminology.  I'm just new to this and I 
would appreciate any help I can get. Thanks