Primary Help

From:  Bert Hickman [SMTP:bert.hickman-at-aquila-dot-com]
Sent:  Wednesday, June 03, 1998 7:21 AM
To:  Tesla List
Subject:  Re: Primary Help

Tesla List wrote:
> ----------
> From:  Michael Andrus [SMTP:andrus-at-ccountry-dot-net]
> Sent:  Monday, June 01, 1998 10:13 PM
> To:  Tesla List
> Subject:  Primary Help
> I have a secondary that is 4" PVC and the coil is 18.5 inches long.  It is
> wound with 21 guage wire, enameled.
> The tank circuit is a 15Kv 30ma NST with a .0049 Mf bottle capacitor.
> It uses a RQ gap with 4 gaps.
> My terminal is a torus 4"X14"
> What type of primary would work with this?  I haave tried the following,
> 1) 12 guage house wire 12 turns vert. 8 in. diameter, 8" sparks
> 2) 1/4" copper tube flat spiral 7 turns from 5" to 16", no output
> 3) 11 guage enameled flat spiral 24 turns 5" to 16", no output
> I need a lot of help in this area, Please help.   M. Andrus


All three types of primaries will work. I suspect your problems were a
combination of tuning and coupling. The most efficient primary of the
three will be one made from 1/4" copper tubing. Your loaded secondary
will resoante at around 440 kHz. You need to make sure that your primary
resonates at the same frequency, then adjust coupling for best output.
Chances are your helical primary had the best initial tune and better
coupling, giving you best initial performance. It also may be that your
pancake primary lacked enough inductance.

Make a larger inner diameter flat primary so that you have at least 1.5"
of clearance all around between the secondary and the primary. You'll
need this since to adjust coupling, you'll be adjusting the height of
the secondary versus the primary, and the secondary must be able to pass
through the center of the primary without flashovers. You'll need about
25 uH of primary inductance to bring the system into tune. This means a
10-turn pancake, with an inner diameter of about 7", with turn-turn
centerline spacing of about 0.5" tapped at about turn 9.

Tune the coil at lower power levels (use only half the gaps temporarily)
and tape a small sharp object to the outer surface of the toroid to that
you can judge the sparklength output as you tune. Using trial and error,
adjust the primary tap until you get maximum output. This will be the
proper primary tuning point. Now you can increase power to the maximum
to see if you have other problems. Remove the object from the toroid and
attempt to increase the power level to maximum, carefully looking for
any signs of overcoupling (sparks racing from the top of the secondary
to lower portions of the winding). If you get these sparks, you'll need
to raise the secondary a bit to reduce coupling. Otherwise you can begin
lowering the secondary versus the primary to increase the coupling. You
will reach a point where you get good breakout, with no overcoupling -
you're there! Good luck!

-- Bert --