Quoting Ed Sonderman:

 ES> Coilers,

 ES> ... run into a problem with the capacitor.  It is the one    
 ES> difficult thing to make at home.  I did make two rolled      
 ES> capacitors using aluminum flashing and .0625 polyethylene. 
 ES> I did a good careful job building them.  They both came out  
 ES> at .019 microfarads.  They worked fine for a while until I   
 ES> finally got up to 12kv and tried to run them for several     
 ES> minutes at a time and they both eventually failed -          
 ES> punctured the dielectric. I am convinced that capacitors     
 ES> built like this (with .062 poly) will only withstand about   
 ES> 9.0kv for any period of time.  If you use .062 you need to   
 ES> use two of these in series for 12 or 15 kv operation.  

I certainly won't argue the point here. I have blown my share of
these, including one failure while the capacitor was wired in
series for high-voltage operation (and running a whopping 12kV)
when a flashover from the wiring leapt a connection.

 ES> My problem was that I needed .019 mfds.  So I used one       
 ES> capacitor at a time and eventually ruined them both.  What I 
 ES> really needed to do was to build 4 of these and use them in  
 ES> series/parallel. Another option would be to use .093 poly    
 ES> but the finished value will drop down quite a bit.

Again I will concur.

 ES> I calculated my cost to build these capacitors at about      
 ES> $90.00 each. This is about the time Richard Quick suggested  
 ES> buying a commercial made capacitor. I got quotes from four   
 ES> different companies. Condenser Products Corp. in             
 ES> Brooksville, Florida (phone 904-796-3561) provided the best  
 ES> quote and seemed to be the most knowledgeable. They built a
 ES> custom capacitor for me for $185.00 including shipping.      
 ES> This is cheaper than I could have built it for, it is much   
 ES> smaller than 4 large upright home made capacitors and I'm    
 ES> sure it will take more abuse.  The value is .025 mfd,        
 ES> 15,000v RMS AC rated for pulse discharge - Tesla tank        
 ES> circuit operation.  It was tested to 33,000 volts. They told
 ES> me today the price for this capacitor would be $220.00 
 ES> I just thought I would let everyone know about this.  
 ES> It may seem like a lot of money, but I think it is cheaper   
 ES> in the long run and they do build a great product.

I too own a couple of capacitors from Condenser Products, and I
will agree that these are top flight units rated (though not
guaranteed) for Tesla work. They can be very cost effective (both
in construction time and money). However, consider another aspect
of coiling as well, versatility.

If you go out and buy a single hefty commercial capacitor you are
really locked into a specific range of frequencies and power
levels. Purchasing multiple commercial capacitors of lower values
is not cost effective when dealing with new units. Your higher
frequencies use less capacitance, are safer for many experiments
and test setups, and are difficult to reach with a large capa-
citance. By constructing two, or even better four, homemade
capacitors you can span a greater range of frequencies than can
be easily obtained with a single commercial capacitor. If you
then add a commercial capacitor to your stock of homemade units
you have the ultimate in frequency and power ranges, reliability, 
and versatility.

Richard Quick


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