Re: primary coil increase to 3/8 (.375") From 1/4,1/4 spacing.

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: FutureT@xxxxxxx 

In a message dated 7/9/05 1:56:13 AM Eastern Daylight Time, 
tesla@xxxxxxxxxx writes:


> Hi John,
>
> I broke out a email you wrote in 97 regarding this and notch quench. I
> realize that the increased tubing diameter reduces the r component of the
> impedance and therefore benefits the current capacity. But it seems to me
> that the arc space effects the coupling much as raising and lowering the
> secondary which in turn has an effect on the diameter of the primary which
> in turn has effect on the magnetic field shape.


Hi Jim,

I'm not sure what you mean by the "arc space".  Do you mean the
overall area of the primary or the primary field?  It's true that a wide
secondary may have a wider field, but the measured coupling or
actual coupling is what is important.  This can be determined by
using a computer program such as Bart's JavaTC.


> Are you speaking to the inverse square law here? I am a bit confused as the
> ratio's dimensions often spoke about here that must have some synergy in the
> shape of the field albeit much less than the lower turns of the secondary.
> Am I with you at all here? What effect of this field('s) does this have on
> the inductive rise further up the coil? What conceptually have I misplaced?


I'm not sure which ratio dimensions you're refering to.  Do you mean
the ratio of the primary diameter to the secondary height?  I've
compared very wide primaries and very narrow primaries on the
same coil and the results were the same.  The results (spark
lengths, racing sparks, etc) always depended on the measured
coupling.  Regarding inductive rise further up the coil, this rise
results mostly just from the energy that is supplied near the
bottom of the coil directly from the primary.  The coupling from
the primary to the higher parts of the secondary is minimal.
If you're speaking of the ratio of the width to height of the
secondary itself, this is important because it directly affects
the coupling.  The coupling depends on what portion of the
total secondary is near the primary.  It's true that changing
any of the sizes or proportions will alter the coupling.  My main
point is that usually the coupling is not adjusted by changing
the primary tubing size, although that can be done.  Is your
goal to use a certain size primary in an attempt to get the
coupling correct?  It is true that may work.  I usually just raise
the secondary if needed to get the coupling right.

To give an example, consider my TT-42 coil which has a
rather narrow small primary.  Then consider John Morawa's
coil which is similar but has a very wide spread-out primary.
Both coils behave very similarly in behaviour and results.
There's a link at my website to John M's coil.

John


> Comments welcomed,
> Jim Mora