[TCML] Re: tesla coil help

[Barton B. Anderson]

Hi Ben,

In Javatc the inductance will be good, but the coupling may be off some 
due to the up and down helical situation. The closest we could get is to 
cramp all 14 turns into the 7 turn height area). BTW, make sure the 
primary isn't arcing across the turns. Your up and down method would put 
the highest stress on the two bottom turns near each other. It it arcs 
across, it will rob power.

I did remodel it and yes, .00042uF is the correct value. I showed about 
2.4 Mhz on both the primary and secondary. I cramped 14 turns into the 
1" height using #14 gauge wire in the primary. Looks like you are in 
tune. Something I've noticed on small coils is the existence of the RF 
ground wire or lack of. There is a major difference in tuning simply 
based on lead length inductance as well. Try it with and without the RF 
ground wire on the secondary (just to look for a change). Also, the 
total lead length I used was 15" (that is to and from the primary). If 
yours is longer it can make a big difference. For example, with your 
coil, just an extra 15" lead length results in a 50 KHz change. Small 
coils are why I inserted a lead length inductance into Javatc. For the 
larger normal coils, this is negligible, but for small coils it can't be 
ignored.

Not sure what the smallest TC is. My smallest is 1" secondary form. 
Wait, I take that back, I once wound a coil on a CD spindle (flat bottom 
with a 1/2" post which rose up from the center about 3 inches). I built 
it and a small little MMC array (totally non-standard caps). I tried to 
use a low voltage MOT and ended up frying the cap board). Lost interest 
and went on to something else. I've since lost it (probably ended up in 
the circular file).

Also, I also saw 34 in your message regarding coupling. I figured a typo 
and ignored it. I showed 0.12 in Javatc which is probably close but not 
exact in your case.

Building these small coils are far more challenging than the normal 
sized TC and I personally realized that after trying a few. I even had 
some difficulty with a 2" secondary. The bigger they get, the easy they 
are to get right. But of course, once one exceeds the practical size, 
then the mechanics and cost becomes very difficult and things like top 
loads are not so easy, nor are the forms, nor is the power, nor is the 
gap, etc.. etc.. To keep big coils at a reasonable cost, one must get 
creative.

Take care,
Bart

Ben Sneath wrote:
>> (I'm not sure I understand the primary configuration). But,
>>     
> if it's 14 turns >at 2" height (boy a picture would help
> here)
>
> Bart,
> the primary is wound upward 7 turns them back down 7 turns
> over the outside of those first 7, the total height is 1
> inch high, also does anyone know how small the worlds
> smallest tesla coil is? as for the delicate tuning, well, it
> i hard to get it into proper tune but it can be done
> (although a pain at times).
>
> Resonance,
>   
>> You're mis-using JAVATC. 34 is not correct. Coeff. of
>>     
> coupling can never >exceed 1.0
>
> you must have misread that. my original message said 0.34,
> not 34.
> and i will be building a 3.5" coil as soon as i can get my
> MOT supply up and running. 
> btw: i do use JAVATC to desgn my coils, from the ground
> up...
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