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Capacitors



>The color of the spark always tells me a lot about a persons capacitor.  
> purple or purple-violet tells me the fellow is a novice and his caps are 
>at the very bottom of their performance curve.  Brilliant pretty blue 
>sparks are better but indicate high loss in the tank capacitor is still 
>taking place.  Rich blue-white sparks indicate only satisfactory 
>operation.  Snow white arc channels only fringed in brilliant blue 
>indicate top performance operation and snyergistic tank operation and 
>energy transfer.  With enough power input, to over come losses,  Mylar 
>and mica can give quite impressive sparks.  Both will heat rapidly and 
>only the Micas stand much chance of survival if long runs are the norm.

Thank you Richard for this posting, you explain a symptom that I am getting,
namely the purple-violet sparks of the novice.  

I must admit I thought that I had built a good cap having made it from foil,
poly sheet and oil, using the extended foil ends to form the terminals.  I
understand that the advantage of the extend foil ends allows terminal
connection down one side of the cap plate thus keeping self inductance low.

My question is how do you make a good cap?  Or is the bad performance due
to some other factor?   How much does conductor size of the primary tank
circuit make a difference?   Size of toroid (14" on a 7" coil), operating
frequency (220KhZ).  What I do know is that the sparks are not white.

My plan is to make as many mistakes on my current coil in order to learn
the most from the experiance.   Work has just started on a 10" coil which
I hope to fire at 10KVA.

Any comments most welcome.

Julian Green