Re: toroid dimensions

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <FutureT-at-aol-dot-com>

In a message dated 9/25/01 3:54:07 PM Eastern Daylight Time, tesla-at-pupman-dot-com 
writes:

> Hi all,
>  Is there an optimum physical size for the topload terminal?  

Jeff,

You bring up an interesting question which has been addressed
before on this list.  There is indeed an optimal range of sizes.
A number of factors affect the size requirements.  For example,
some folks build a TC using a 15/60 NST, and they obtain only
22" sparks or so with a 4" x 16" toroid, because of design
compromises.  Such a coil may not be able to give longer sparks
even with a larger toroid.  Yet, other folks build coils using a 
15/60 NST, and obtain 62" sparks.  Such a coil will benefit
from a larger than 4" x 16" toroid.  A 6" x 26" toroid or larger
may be of use for such a coil.  A toroid should not be selected
on the basis of coil-tuning considerations.  Tuning should be done
by adjusting the primary tap position.  The toroid should be
selected based on the expected spark length from the coil.
If the toroid is too small, you'll get multiple streamers, but they
will be short.  If the toroid is too large, you'll get only one streamer,
but a breakout point may be needed to permit breakout.  
A toroid of the proper size will give just one or two streamers,
and will breakout without a point.  This will give longest sparks.
Some folks prefer to use a slightly smaller toroid to get more
streamers.  It is not necessary to measure the frequencies
for tuning.  The computer results will be close enough.  Just
tap the primary in different spots by trial and error until the
longest sparks are obtained.  A coil which uses a higher
break-rate, can use a smaller toroid for a given spark length.
I use a 4" x 13" smooth toroid on my TT-42 TC, which gives
42" sparks from a 12/30 NST.

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John