Re: 6 inch coil

> But now we are talking about reaching for spark lengths that are 
measured in
> feet, not inches.  And we are talking about a power supply that will 
cost you
> aroung $1000-$1500 to put together for these higher power levels.  

Not neccesarily - if you frequent hamfests, etc... and don't try to buy the 
things new, you can get by on a lot less!  You should be able gang up 
neon sign transformers up to around 3kVA, and if you scrounge long 
and hard enough, you will eventually find a surplus potential or pole 
transformer that will take you well into the multi-kVA range for between 
$50 and $200.  Case in point - I recently bought a 14.4kV, 2kVA rated 
potential transformer that should be good up to 3kVA or possible a little 
more for $60.  With my $90 hamfest 30A 240V variac (that will run 30A 
forever and 50A for a few minutes easily), a homemade variable 
inductor to keep the breaker box from melting (that will probably run me 
about $30 or $40 when complete),  some heavy-duty contactors, and 
some misc. support stuff, I should be good to go for under $300.  To 
move to higher power levels will just need to get a higher current 
transformer...my control electronics should be just fine for about 6kVA 
continuous and up to 10kVA intermittently.

As stated - until you start aspiring to multi-kVA levels, coils can be dirt 
cheap and you're going to spend more time than anything.  The coils I 
have built until now have cost me under $40 complete (including my 4" 
dia., 16" long coil with a terrible primary that puts out 20" sparks on a 
good day).

Steven Roys (sroys-at-radiology.ab.umd.edu)