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First light, and a poor performance


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From:  RWB355-at-aol-dot-com [SMTP:RWB355-at-aol-dot-com]
Sent:  Monday, August 24, 1998 9:53 PM
To:  tesla-at-pupman-dot-com
Subject:  Re: First light, and a poor performance

You wrote in an email: 

From:  Steve Rodway [SMTP:Legion-at-legion-elec.demon.co.uk]
Subject:  First light, and a poor performance

 Just fired up my new TC for the first time tonight
<SNIP>
Power supply, 11 kV (rms) polepig with resistive ballast made of 4Kw
of heating elements filter consists of 2x20mH inductors and a 1.7nF
bypass cap. Main tank capacitor is 7.42nF and the primary coil is a 30
degree inverse conical with 12 turns of 1 mm wire 7 mm apart. The
primary is spaced 20 mm from the secondary and the bottom turn of each
coil line up. The gap is 6x0.5mm tungsten carbide static gaps.
The secondary is 4" dia and wound to 16.5" with 0.56mm enameled
wire, there are around 660 turns giving an inductance of 11.4mH and a
capacitance of around 8pF.

<SNIP>
 
Comments:

1.) Your cap is a bit small it should be around 8.75 nF, although you could
 get away with it.

2.) I think a flat primary would be better for your setup. The cone coil does
 not offer you any advantages in this setup

3.) The wire gauge you are using for your primary is WAY TOO SMALL. Try 1/4 or
 1/2 copper tubing.

4.)Your coil could probably produce better results with a bigger secondary.
 Try something like 6" or 7" times 24" to 30" long (winding length) plus
 another 1"-1.5" on the top and bottom (no wire). Use a wire gauge that will
 allow you to wind somewhere between 800 and 1000 turns. Thicker wire/low turns
 are better because you will decrease the resistance and increase the "Q" of
 your coil. The coil you built would be better suited with a 60 to 120 mA NST.
 The wire gauge you used works out to AWG 23, which IS okay for the coil you
 WANT to build.

5.) If you use a top capacitance, you should keep away from any metalized
 plastics, as the RF power is great enough to melt the plastic (which you saw).
 Try ducting hose or elbows to make your toroid, or at least use aluminum foil
 on plastic stuff. The "metal" on the top capacitance you used is probably only
 a couple of mils thick.

6.) I would try to go for more spark gaps. 6 is a little on the low side.

7.) 4 kw input power should get you at least 90-100" sparks, when properly
 tuned. I get 6" sparks from a thrown together coil with 200 watts of input
 power and I didnīt tune it or anything. E.g. I used caps that are way too big
 (I just had em on hand)

8.) FORGET the 1/4 wave stuff. Alas, another poor soul who fell (like I DID
 TOO) for the old theory. Basicly you will have to design your coil the other
 way around. Design your secondary first, calc at what freq it resonates (using
 Wheeler and Medhurst) and the build your primary circuit to fit.

I hope I didnīt "hit" you too hard. But you learn by doing and that means
 making mistakes, too.

coiler greets from Germany,
Reinhard