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4" coil

Hi Tom,

<<  A 6" coil can take a lot of power and is more
<<expensive to make than say, a 4" coil.  A 4" coil can take a lot of power
still
<<and be considerable more managable for a beginner.  Coiling can reach DEEP
into
<<your wallet.

<<I have a small 4" coil that puts out 24" discharges into free air, and its not
<<even close to being maxed out.  All I have to do is feed it more power.  It
<<should be capable of at least 36" discharges, and I'm being conservative here.
<<With that much spark, It will require a space of at least 7 feet in diameter.
<<That's 3' one one side, 1' of toroid, and 3' on the other. 

<I would be interested in getting some specifics on this 4" performer.I too
<built a 4" coil and was dissapointed with the poor showing (missinformed).
<The list has been great for educating me where I went wrong but I would be
<interested in hearing how you achieved what I failed in.

Well, there's no secret to it.  When I first built it, it didn't perform like
this.  As you may know, much of the performance gains are made in the primary
arragement, specifically the power input, capacitor and spark gap arrangement,
which are critical.

The first thing I would look at is my transformers.  What kind of power are you
putting in.  If you've got over 1000 watts, you should be seeing 2' arcs.  If
you have the power, look at the spark gap.

Are you getting good quenching from your gaps?  That is critical.  It is
impossible to tell by just looking.  I am using vacuum gaps (which I recently
had a problem with, but RQ helped me correct it) which "blow out" the gaps very
quickly to keep the primary from bleeding back.  I repeat, quench time is
critical.  When I first went to vacuum gaps, my spark length increased by at
least 50%.

Lastly, what kind of capacitors are you using.  I am using a commercial pulse
cap and some homebrew vertical plate pulse caps.  Good, low loss capacitors make
a big difference too.

As far as the 4" secondary coils I have, there is nothing special there.  One is
even wound directly onto PVC, without sealing it, althought its performance is
off from the other by a few inches.  But even the one wound directly on the PVC
gives nice violent discharges; at 800 watts it give around 16" violent
discharges.

The primary on this old coil is a bundled type.  While it doesn't give the
greatest coupling, it works pretty good.

I'm not in favor of using these inefficient designs I have described above, I
just wanted to point out that good output can be acheived with less than ideal
primaries and secondaries.  I would never build one like these now.

So as you can see, I believe the secret to good output starts in the tank
circuit.  If you don't have a good setup there, you'll not get good output, no
matter how well you build your primary and secondary coils.

Scott Myers