[Prev][Next][Index][Thread]

PRIMARY COIL

Quoting Mark Conway:

 MC> Hi Richard,

 MC> I've just had a mammoth session cutting out all the bits of  
 MC> plastic for my flat plate cap - next weekend I should be     
 MC> able to add the foil and hopefully complete the cap.  

Flat stack plate capacitors are fairly easy to make... but they
are extremely tedious, with hours upon hours of time required for 
a good construction. I am sure you have already found this out.
The advantage though is that these caps are the best design for
high performance Tesla coils. Given the lack of thick plastic
sheet there in New Zealand, you really don't have much of a
choice.

 MC> After hearing of Ed Sonderman's success with his coil I      
 MC> really want to finish off my one. I just hope that my main   
 MC> cap will hold up - I am trying to keep everything really
 MC> clean during the construction and I figure that it should    
 MC> theoretically be able to withstand up to 26000 volts. If it  
 MC> doesn't stand up to the high voltage its going to be really  
 MC> frustrating! 

A spot of good news for you perhaps... Ed Harris posted a polymer
reference which stated that the thinner the dielectric, the
higher the breakdown strength per mil! This may be yet another
reason that the flat plate caps work so well.

 MC> After the cap all I will need to complete are the            
 MC> suppression caps and the primary coil. I have the soft       
 MC> copper tubing for the coil. I notice from your postings that 
 MC> you recommend making a "comb" out of plexiglas for the       
 MC> copper tubing to sit above the wooden support. I see in the
 MC> photo from Richard Hulls guide to the Colorado notes that    
 MC> Richard Hull also uses this method but I remember that in    
 MC> your video, the primary coil you use is on wooden supports   
 MC> which you say were heavily dried and polyurethaned. Is using 
 MC> such a primary coil almost as good as using a high Q plastic 
 MC> support? The reason that I ask is that I will be able to
 MC> make the primary coil support a bit faster if I can just use 
 MC> wood alone. 

Plastic supports for the primary coil are preferable: but you can
"kiln" dry the pre-cut wood parts in an oven set to low temper-
ature; let the parts dry for 24 hours, and them assemble the
dried parts with a water free two-part epoxy. Once assembled, 
the coil form will then require about five or six heavy coats 
of polyurethane to prevent moisture reabsorbtion. 

The reason I state this (and have done it for a couple of my
older primary coil forms) is that the primary conductor is
generally not in intimate contact with large areas of the coil
form. Certainly the construction is very different from a
secondary coil where plastic forms are a must.

High tank circuit Q's and sharper tuning will be achieved with
all plastic coil forms. Remember, even PVC is better than wood in
the long run. My large primary is a combination of wood, with
plastic "comb" supports, and then later I decided it is worth-
while to spend the money (and time) to build primary coil forms
using all plastic parts. The main reason is that you cannot come
close to removing all of the moisture from wood.

Richard Quick

... If all else fails... Throw another megavolt across it!