Re: Secondary Construction

>RQ> In a high performance design, properly driven, the secondary coil
>RQ> is easily capable of producing sparks that greatly exceed the
>RQ> physical height of the secondary coil. In other words, your coil
>RQ> may be 20 inches tall producing sparks that are 30 inches long. 
>RQ> Under these conditions an "open" or uncapped coil will almost
>RQ> certainly fail. All of the electrical failures that I have seen
>RQ> occurred inside of the coil form. The failures resulted in
>RQ> sidewall perforations, arc scoring, and carbonization of the coil
>RQ> form. I have never been able to successfully repair a coil once
>RQ> it has failed in this manner.
>Point taken, but...
>Can anyone explain why sparks would prefer to travel down the inside 
>of the former (winding) rather than the outside ?

Well, the inside is about the shortest distance an arc would have to travel
to find an earth.
The sparks do 'like' the outside as much, but when arcs flash on the
outside, they will probably 
hit something else........hopefully. I dont think ive ever seen an arc
strike the base winds from the outside come to think. 
Its just that this kind of arcing destroys your secondary. I had one which
failed this way, and by time I figured
out what was happening the arc had burnt an inch long cut up the base. It
started at the bottom turn and worked its way up from turn to turn,shorting
the winds as it went and 'raising' the earth. This coil was not sealed. I didnt
really imagine getting arcs longer than the winding height at that time, so
I suppose it was good news in a
 way.      :) It can also be hard to see this problem. Just listen for the
muffled arching noise       :)