RE: My second coil attempt, advice?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Lau, Gary" <Gary.Lau@xxxxxx>

Hi Scott:

I would agree with your suspicion that your gap is the weakest point.  I
would suspect any gap that has a small or pointed arcing surface.  With
the power that a 6-pack MOT PSU packs, I agree that a rotary gap is
needed, but I'm not sure that you'd see a benefit with a sync gap.  With
that much power available, I think you need a higher break rate than
120BPS, so I'd consider an async RSG.

Another suggestion would be to consider increasing both the primary and
secondary inductance to increase the primary surge impedance and cut gap
losses.  But I'd start with the gap.

Regards, Gary Lau
MA, USA

> Original poster: "Scott Bogard" <teslas-intern@xxxxxxxxxxx>
>
> Hello all,
>      I am a relative newbie to the list, and I have recently finished
> my second Tesla coil (60Hz AC system), and the output is Ok (strikes
> 38 in, and streamers about 5 ft tops) but I have seen very similar
> coils put out as much as 8 ft or more.
>      Here are the specs,
>      Power supply:  6 MOT stack, center tapped ground (~12kV out 120V
> in ?? amps, I don't have the tools to actually measure this) no
> variac, full power or nothing.
>
>      Ballast: 1 MOT (shorted of course).
>
>      Tank capacitor:  75nf Maxwell, tested at 81nf (so the label says
anyway).
>
>      RF filter:  ohmite resister 50 ohm "chokes" filled with 4
> welding rods for "inductance" and some ceramic capacitors about 600pf
> (I don't know if it works or not, but there isn't much interferance
> on our TV unlike my old (smaller) coil) and safty gaps to ground (I
> don't use a mains ground at all, I use a seperate peg in the ground
> from the RF ground for the MOTs and safety gaps).
>
>      Secondary: 6in PVC 22AWG wound 31 in (+-1160 turns) three super
> thick (uneven) coats of polyurethane.
>
>      RF ground: copper pipe pounded in about 1.5 ft (the ground may
> still be frozen down there).
>
>      Top load:  2 aluminum flex duct toroids covered in foil tape,
> 3in*15 and 7in*21 (I tried a large 11.75*42, but got no streamers
> breakout with it connected).
>
>      Primary:  1/4in copper (refridgerator) tubing, spaced .75in
> apart with an 8in hole in the middle for the secondary.  Tapped
> between turns 7 and 8, and sits just a hair below the first secondary
> winding (no racing arcs yet, moving it downward  lowers the
> performance, moving it up changes nothing).
>
>      Wiring: tank circuit-14AWG rated at 15kV, other wire-whatever I
> had lying around (18AWG 20kV, some house wire, and some 22AWG magnet
> wire, run through polyethylene tubing for insulation).
>
>      Spark gap: (probably my performance killer) single blower static
> gap, two brass bolts filed roughly to points (I use pointed contacts,
> because smooth rounded contacts on my first smaler coil, instantly
> gave me terrible (really really bad) racing sparks, and the pointed
> ones gave fairly smooth nice operation,) currantly .75cm or just
> between 1/4 and 1/2 in. seems to give best results.  My saftey gaps
> are set much narrower than this, but they have rounded contacts and
never fire.
>
>      I am building a synch rotary, but it will be some time until it
> is ready, I do however have a much stronger blower on the way (the
> currant one is lousey compared to the one that is coming).  The
> output is Ok but somwhat inconsistant (I am running it outside, and
> it is very moist here right now with snow melt and rain) sometimes it
> will strike the strike rail 38in away while two additional long
> streamers fly out in the air, and then a second later all you will
> see is one tiny streamer 2.5 feet long or so, and it does everything
> in between totally randomly.  Aside from building my rotary gap, is
> there anything I can do to tweak just a little more output out of the
> thing (a breakout point reduces the output, but makes it easier to
> see as it doesn't move around the toroids).  Thank you much
> Scott Bogard.