Re: Some interesting observations ....

[FutureT-at-aol-dot-com (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

In a message dated 7/30/00 7:46:28 PM Pacific Daylight Time, tesla-at-pupman-dot-com 
writes:

> Original poster: "Garry F." <garryfre-at-pacbell-dot-net> 
>  
>  I have built tesla coils on and off starting way back about 1972 and just
>  recently got back into the hobby. One of my biggest problems was not 
knowing
>  how to build rf chokes to prevent feedback through the NST and destroying 
it.
> 
>  Until recently, all the tesla plans I ran accross involved showing me how 
to
>  build chokes using a full page of mathmetical symbols that resembled 
> egyptian
>  hieroglyphics than anything else. I used the plans from sciencefirst 
because 
> it
>  had choke winding instructions in terms of "Wind X guage wire over Y 
length 
> of
>  wooden down of Z length. 

Garry,

I'm glad to hear you're getting back into coiling.  Many folks have
found that using chokes to protect NST's often burns them out 
instead due to unwanted resonances.  I just use safety gaps to
protect my NST's but many folks use resistors, caps, and MOV's
in addition.  I'm very interested in obtaining maximum efficiency 
from my coils.  One of my coils can be seen at:

  http://hometown.aol-dot-com/futuret/page1.html

I use a 12/30 NST for power, with a small sync rotary gap, a
commercial Maxwell cap, and a spun aluminum toroid.  This gives
42" sparks maximum.  I use what I call the "Six Keys" for 
efficiency.  These are:  Relatively small secondary, thin secondary
wire, sync rotary running at 120 bps, lots of primary turns, high
quality properly sized capacitor, and a properly sized toroid.

I first realized the benefit of using thin secondary wire about 10 years
ago, when I was just getting seriously involved with coiling.  I had just
wound a 7" by 19" secondary using 34 awg wire, and got 40" sparks
from a 12/30 NST, using a simple static gap.  The coil must have been
a little overcoupled because I kept getting burning on secondary wires.
Since the secondary was ruined, I decided to rewind it using thicker
wire since that's what folks recommended.  They recommended 22awg
wire, but I only had 25awg, so I used that.  Well I lost about 3" of spark
length.  Imagine how much I would have lost if I had used 22 awg wire?
After that, I compromised by using 28awg wire, and I've been using
mostly that since then.  I did do another comparison recently and
wound a coil with 20awg, but I lost 10% of spark length.  I think that
many coilers could gain 10% by using thinner wire on their coils.
It is a method that is not well known since as far as I know, very
few folks have made a direct comparison.  The only one I've heard
of who has made a comparison (other than myself) is Richie B.
He removed his 1000 turns of wire from his secondary and rewound
it with 1500 turns of thinner wire, and gained 10% spark length,
and the sparks were brighter, more active, etc.  He said it gave the
coil a whole new character of power, and excitement, which matches
what I've seen in my work.
Of course a larger coil will need thicker than 28awg wire.  In any
case it's all quite fascinating.  It seems that the thinner wire, although
it has higher losses, permits the secondary to be quite small which
concentrates the energy in the self C of the toroid, instead of so
much in the self C of the coil itself.  The real key of the thin wire
though is that it lets more turns be used.  I use about 1600 turns
on the secondary.  This demands that more turns be used on the
primary, which raises the surge impedance of the primary tank,
and reduces gap losses.  Most of the losses in a TC are in the
spark gap, so any efforts to reduce that have a great benefit.  The
small secondary with many turns might match impedance-wise
better to the sparks too, but there are many controversies in that
area.  Well, I'm rambling on too much.  I look forward to hearing
more about your coiling results as they become available.

Cheers,
John Freau