[TCML] Why don't big Tesla coils use helical primaries?

[Futuret]

You can use a helical primary if you'd like.  You can use Bart Andersen's 
excellent JavaTC program to try out various primary diameters to get a suitable
coupling value.  By close winding the insulated wire, you can get a compact
primary coil.  On one such coil I built, I had to make the primary about 10"
or more in diameter, for a 4" secondary to get the right coupling, or maybe
I was using a 6" dia. secondary, I can't remember but JavaTC will answer the
questions.  I think I still had to raise the secondary some.  I was getting at
least 40" sparks from that coil.  The efficiency is the same for a flat primary
or helical primary.  The efficiency is most affected by the type of wire on the
primary; wire gauge, solid or stranded, etc.

Cheers,
John





>

> Hello,

> so I was just wondering why no one uses helical coils with insulated wire

> like this: http://www.johndyer.com/MakerFaireJD06.jpgwhen building big

> static gap tesla coils.

> I have seen tons of small sgtc's with a primary like that, but it seems

> that with bigger sgtc's people always use copper tubing and carefully space

> them in a flat or conical spiral.

> I don't understand this.  <snip

> thanks for the help!