I have a small 4" coil that puts out 24" discharges into free air, and its not
even close to being maxed out. All I have to do is feed it more power. It
should be capable of at least 36" discharges, and I'm being conservative here.
With that much spark, It will require a space of at least 7 feet in diameter.
That's 3' one one side, 1' of toroid, and 3' on the other. My 6" diameter coil
can produce very little more spark than this 4" coil with the same power supply.
It gains about 3-4" (and a little extra violence) of spark with the same power
supply. You will spend at least 4X the money to build a 6" coil. The advantage
to a 6" coil is that if you decide to go to power levels in excess of 1.5 KVA,
you will have a coil that can take it without breakdown, if it is well built.
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. Saftey is
also an issue. If you are still going to go to the 6" eventually, I would still
suggest you build the 4" first. If you make a mistake on it, you are out a lot
less money, and time. Trust me, you won't be disappointed when the sparks are
flying from a 4" coil. I'm not.
As far as wire on the secondary coil former, solid enamelled magnet wire should
be used. It is available form most electric motor repair houses. If you do
decide to build a 6", 22 gauge magnet wire is a good choice. Download the
COILBLD* series, by Richard Quick, from the links on Bill Beaty's Hompage. It
is a good reference to use. I would also suggest you download TESLAC and some
of the other programs from there. These are design program to use in building
all of the companents of a Tesla coil.