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Varying the size of the topload will have certain effects.  For example a smaller
topload will tend to give multiple shorter sparks.  As topload size is increased,
at some point you'll get just one spark streamer.  If the topload is a little smaller
than that you'll get two streamers which may alternate side to side.  As one
streamer grows, the other will shrink.  I like that effect.  If the topload is made
even larger, it can get to the point where the sparks cannot break out at all
unless you add a breakout point or rod.  

The above pertains largely to smooth toroids.  If a toroid is rough or corregated
then sparks will tend to emit from any sharp edges or bumps.  

When a topload is extra large, the sparks may look somewhat purple or
fuzzy, not as blue and crisp.  

Proper topload size is mostly determined by the Tesla coil input power and
efficiency, as well as by the other factors mentioned in the above paragraphs.
For example in my TT-42 table top coil which gives 42" sparks from a robust
12/30 NST, I use a 4" x 13" spun aluminum toroid.  Using this size, I obtain
sparks which alternate side to side for the most part.  If a smaller 3" x 10"
toroid is used, then maybe only a 30" sparks would be obtained, but there will
be multiple streamers.  I use a 120 break per second synchronous rotary
spark gap for high efficiency.  Many simpler 12/30 NST coils would need
to use a smaller toroid for best results.  

A toroid is the best overall shape for a topload, but coilers sometimes
use other shapes such as a sphere for various reasons.  

The toroid should be raised a little above the secondary winding top, but
not too much, maybe just an inch or so above.  Too low limits the spark
output, too high may cause too much corona to appear at the top turns
of the secondary.  

I often place a smaller toroid below the main toroid as a corona suppression
ring.  There should be some space between the two toroids to obtain 
the most overall topload capacitance.  However space limitations can
sometimes constrain the design.

There's a trend lately to use toroids made from multiple tubing rings of
different diameters to form an open framed design.  This is great for
reducing the weight of large Tesla coils.  Some large coils even use
chicken wire spread over foam or plywood supports, etc.  

Toroid size will generally scale as the square root of the input power,
adjusted by a suitable factor.  For example a 600 watt efficient 
coil might use a 4" x 13" toroid.  And a 10kW coil might use a 
12" x 60" toroid.





-----Original Message-----
From: doug <doug11642@xxxxxxxxxxx>
To: tesla <tesla@xxxxxxxxxx>
Sent: Sun, Nov 29, 2015 10:52 am

Hello; Can some of you,more learned than I, Coilers give me some insight on proper TOP LOADS?  such as, results of too much top load, proper placement of multiple top loads, and any other pertinent information and advice when designing a top load for any given coil.
Thank you, Doug J 
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