Re: Questions from a newbie in Australia

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-uswest-dot-net>" <jimlux-at-earthlink-dot-net>



Tesla list wrote:
> 
> Original poster: "Stacy Gillett by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <sgillett-at-hotmail-dot-com>
> 
> Hello all...
> 
> I'm a uni student from Geelong (a town near Melbourne in Australia), and I'm
> planning to build my first coil.  I've got most of the parts together, but
> I'd like to ask some questions before I start putting anything together:
> 
> 1.  Instead of a single NST, I have two 15/25 units.  The problem is that
> they both have one side of their secondaries shorted (in effect, they can
> only put out about 7500V each).  The guy at the sign shop I got them from
> said that I could get 15kV out by tying their centre-taps together and
> taking the HV from each of the good secondaries (the bad sides are not
> connected to anything).  Assuming that I had the primaries wired up in
> parallel and in the correct phase, would this arrangement work?

Yes... but.. you might try the heat and shake technique to fix the shorted
sides, then you'd have a 50 mA unit...  Sometimes the NSTs just develop a
carbon track or other small short internally, as from a crack in the tar
used to insulate them.  Heating the thing up (gently) so that the tar can
reflow might fix the problem. Ignore this if they are the newer epoxy
encapsulated variety.
> 
> 2.  I'm planning on using a 4" x 20" PVC secondary form wound with #22AWG
> magnet wire.  With this size secondary, what would be best in terms of
> coupling: a flat primary or a saucer primary?  I've heard that for the
> smaller diameter secondaries like mine, a saucer is better, but a lot of
> people seem to recommend the flat primary.

Flat primaries are much easier to make and I don't think there is any
signficant advantage in the saucer or cone shaped.  If anything, they may
cause overcoupling.

> 
> 3.  As I can't really afford a Variac at the moment, I was planning on using
> a 100W light globe in series with the mains input so as to lower the NST
> output voltage until I had tuned the primary.  Quick and dirty though it is,
> is there any reason why this wouldn't work?  If it would, is 100W in the
> ballpark for the globe wattage?

Should work just fine... if you like you can start real low with a 25W
bulb, and gradually work your way up.  The NST should be drawing in the
area of 300-400W, so with the 100W bulb in series, your AC voltage will be
down around 25V. You might want to put a few bulbs in parallel...

> 
> 4.  At these power levels (~375VA), is there any real benefit in cooling the
> main gap with a muffin fan or similar? (My main gap will be 11 x 3/4" x 3"
> length copper tubes, .028" spacing)

YES.  Not so much for bulk cooling as to spread the sparks out across the
surface of the tubes.
> 
> Although these are only fairly minor queries, I'd be grateful if someone
> could clear them up for me.
> 
> Thanks,
> Stacy Gillett
> 
> P.S.  Are there any coilers from the Melbourne/Geelong region on this list?
> It'd be good to hear from someone local who's actually got a coil up and
> running, as my parents tend to think I'm crazy doing this stuff by myself :)

You ARE crazy.... but then, so are we all.