Puncture voltage

quoting Jorge <al263636-at-sal.itesm.mx.pupman-dot-com>:

> Im fairly new on building Tesla Coils, i recently built a
> small  one, it uses a 9000, 30ma neon sign transformer. My
> problem is  with the cap, i live in a small town and theres no
> where i can  get the poly to build the caps, so instead i used
> 1/8" window  glass, i sumerged the cap in oil and i also
> spreaded some in  between the plates, my question is ? Can the
> cap hold and for  how long ?.

You are pretty much right on the edge of the dielectric strength
of this cap with a 9000 VAC input into the tank circuit. But if
you take a few simple steps to reduce the peak voltage I see no
reason why the cap should fail right off.

1) Use a variac to control the input voltage to the neon. A       
   variac is your best defense against disastrous failures,       
   especially in new and/or out of tune coil systems. The last    
   thing you want to do as a beginner is to throw line voltage
   at the step-up transformer right out of the gate. I never
   do. A small variac can be purchased from a surplus catalog
   or surplus electronics dealer and shipped UPS. If you can't
   locate/afford a small variac then consider using some          
   ballasting resistance in series with the primary on the neon.
   You can reduce the value of the resistance as you get the      
   system tuned in, then shunt it with a switch while the coil    
   is running to bring the system up to full power.

2) Don't open your tank circuit spark gap up too wide. Start out
   with the gap adjusted very narrow. You can verify that the     
   coil system is processing power by observing the glow of an
   unconnected fluorescent tube held near the discharge terminal.

As the coil system is brought into tune you can increase the
power by leapfrogging in small steps until good spark is
produced. First dial up the voltage on the variac a bit (or
reduce the value of the ballast resistance) then open the spark
gap up a notch. This procedure should be repeated over a period
of time (make all changes with the power off and all capacitors
discharged) while the coil is gradually tuned. This allows the
new components to settle in before they are stressed.   

> ... I'm new at this some and im a little nervous turning on the
> coil and have the cap blow up. 

In the end this cap will likely fail, but don't let that dis-
suade you from turning the coil on and getting it tuned up and
sparking. If you follow the guidelines above you should have no
difficulty in getting results from the coil before something
smokes. To get a reliable 10 KVAC glass capacitor from regular
window glass I have found you have to use two capacitors in
series, as a single thickness of standard window glass is not
rugged enough. While you are playing with your coil, you can
think about your next generation capacitor.

Also, about blowing caps and trannies, don't get too
apprehensive: if you are not blowing capacitors and trans-
formers then you are not really coiling. Equipment failures 
are almost a "right of passage" to Tesla coilers. 

Richard Quick

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