[Prev][Next][Index][Thread]

Re: Top Load Optimizing - Q?

Hi Jim,

At 12:28 AM 03/20/2000 -0500, you wrote:
>Terry,
>
>Thanks.. you just cleared up quite a few misconceptions a newbie can make
>(this one did anyway) concerning efficient coil design.  That still leaves
>one unanswered question however, one I was hoping Rodney's original article
>answered.  Others on this list seem to suggest a coil should run the largest
>possible torroid a coil's design will support, and that the longest
>streamers will result from a large-as-possible top load to delay breakout.
>
>So... how do I predict the (nearly) optimized torroid size for my coil given
>my power source, tank capacitance, secondary and primary design?  Is there
>an accepted way to do this beforehand, or must I simply try larger torroids
>until I can either no longer tune without adding tank capacitance,(run out
>of primary turns) or until I can no longer achieve streamer breakout?   << 
>Give me a quick hint here.  Thanks.
>
>
snip...

There is no calculation or program that will predict this.  This is all
experience but there are a few hints...

If the toroid is "too small" you will get many small streamers instead of
one long streamer.  So for long streamers you want a large toroid.
Apparently, you can get a toroid "too big" but it is pretty hard.  I would
try and get many turns on the primary so you can tune down to lower
frequencies no mater what.  My 15kV/60mA coil has 100 feet of tubing and 20
turns on it.  My small 9kV/30mA coil has 50 feet of tubing and 13 turns.
Since the primary coil tap is the only easy way to tune a coil, I am sure
to give myself as much room to play there as possible which means a lot of
turns on the primary coil.  Since I match the primary capacitor to the NST,
I really can't change the capacitance for tuning so the primary coil is all
I have to tune with.  I just got a big spun toroid from Finn and I still
only need to change the primary tape to tune it.  So I would try and make a
big toroid that does not look too overwhelmingly large for the coil.  A
smooth spun toroid gives longer arcs than the dryer duct type but the duct
toroids are the right price...  Perhaps others have some better rules of
thumb than I on toroid sizing.  I just use the toroids I have around and
can find parts for.  I really don't think about what size is best.  Rather,
I go over to the hardware store and see what the largest and longest size
duct they have is and that determines the size of my toroid.

There are people who have gotten terminals so big that they will not
breakout.  However, they just place a little nail on it and away it goes
with great results.

I am sure others will have thoughts too on the "optimal" toroid size for a
given coil...

Cheers,

	Terry