Re: new coil specs (sec width considerations)

In a message dated 99-10-29 10:12:48 EDT, you write:

> My major question is what is the relationship of sec. diameter to a)the
> spark length and b) the input power needed?  In my case I'm deciding
> between 6" and 8" PVC.  Right now I have only one 12/60 NST but plan on
> getting more soon.  I have MMC capability between 5 nF and 30 nF.


All the relationships are indirect, and stem from practical aspects
of; coil breakdown, for certain (too short) secondary heights, reasonable
aspect ratios, for suitable coupling, Q, losses, inductance, tuning,
frequency, etc.

You could use either diameter of secondary, but if you want to use
more power in the future, then the larger size is better.  The larger
size can be taller, use thicker wire, and can handle more power and
therefore give longer sparks, i.e. a bigger TC.

Secondary height is more immediately important than width, since a
too short secondary will break down when long sparks are produced,
esp if the large bang, low break rate, approach is used.

You probably don't want to go more than 1:5.5 for the aspect ratio;
figure a a 6" dia coil X 5.5 = 33" high.  A coil of this height can easily
give let's say 72" sparks.  If you figure a 8" dia coil X 5.5 = 44" which
can easily give 96" sparks.  In other words, it's all in proportion.  

BUT, you can always make the coil wider anyway, for instance 8" dia
X 33" tall, but this will limit the sparks to 72" in the example.

But let me make one thing perfectly clear, I am NOT saying that a
33" tall secondary can only give a 72" spark.  It can give a much longer
spark in a careful design.  Richard Hull's Nemesis TC's secondary was
I think 45" long, and it gave 180" sparks.  I gave the 72" figure and others
only as examples.  Again it will depend on the bang size, more than on
the spark length.  And there are of course other factors.  It is bang size
not power input nor spark length that determines the needed secondary
height to prevent breakdown.  

Another example;  My TC which gives 64" sparks uses a 6" by 24" 
secondary, but when I install a 4" by 23" secondary wound with the
same wire thickness, it still gives the same spark length.  The diameter
doesn't matter.  However this coil is running near the edge of breakdown
because of the low break rate, large bang method I use.  However if I
made the coil form longer, this would help prevent breakdown.  If I
make it longer, then it should also be wider, so I would have to use the 
6" dia, not the 4".  If I raised the break rate, then the bang size would
be smaller for a given spark length, and the coil would not break down,
but it would not be as efficient either it seems.

Regarding the sync gap construction.  I posted some info a few days
ago regarding motor types, modification methods, etc.  There are
some websites that show the method.  You may want to visit my
website at:    http://members.aol-dot-com/FutureT/index.html
I don't show the mod method there, but I show a photo of a sync gap
I made, and some data on it.   

John Freau