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Rectifying Action? Might it be that simple?
Hello all,
Some of you might remember my post some time ago where I reported that I tried
using a combination Cu-tubing and AL spark gap. During the testing of 3.3" TC
I got longer sparks from the coil using this spark gap setup than compared to
a similar pure Cu spark gap (same total gap width, same number of gaps).
After a preliminary fire up of my 8" coil (I just couldnīt resist, even though
I have read lots of comments on using (or better NOT using) AL in RF circuits)
I once again found that using the AL material in my gap increased the TCīs
output spark length noticeably. It didnīt double the output spark length (I
wasnīt expecting it to), but it DID increase the spark length a measurable
amount.
After a somewhat longer talk with Mike Hollingsworth on the phone he came up
with an interesting theory which I would like to share with you and hear
comments on:
Mikeīs theory (it made sense to me) states that the Al builds up a deep
reaching oxide layer on the Al stand-offs after a few minutes of operation and
this oxide layer stays put.
This would compare to my data: The new AL gets a sand-blasted look after a few
seconds of operation. After that, it doesnīt change in appearance and the
erosion of the material doesnīt seem (visually) to continue.
Anyway, now comes the interesting part. Mike (and I do, too, now) thinks that
this "AL-oxide layer to copper tubing" part of the gap acts as a sort of
rectifier. This would allow the current to flow in one direction only. Meaning
that as soon as the AC voltage reverses, the gap stops conducting almost
instantly, allowing me to achive good quenching. I know you can make an easy
rectifier using a metal-to-oxide barrier, which allows the current to flow in
one direction only.
Could it really be that easy?
Coiler greets from germany,
Reinhard