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Please Help



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From:  Bert Hickman [SMTP:bert.hickman-at-aquila-dot-com]
Sent:  Wednesday, August 19, 1998 7:06 AM
To:  Tesla List
Subject:  Re: Please Help

Pete,

A belated welcome back, Pete! The main problem appears to be that the
main gap spacing of 0.12" is limiting your coil's output. You should be
able to increase the gap to at least twice this length with a 12 KV
source. Do so gradually though, since you are also most likely
overcoupled at your present secondary position. Even with the current
gap setting you might find that elevating the secondary improves
performance, since an overcoupled system tends not to quench properly,
reducing output. Also, you may also want to force air through the gaps
if you're not already doing that to improve cooling and quenching
performance.

As you increase power by adding to the gap spacing, pay particular
attention for signs of any racing sparks between sections of the
secondary winding (to itself). This also means that you're overcoupled
and will need to further elevate the secondary.

A larger toroid will eventually be necessary to get the secondary
frequency down a bit plus and to obtain higher hold off voltage. This
will allow you to use more turns on the primary, which should also
improve your system's efficiency. Try going to a 3 x 12" or so, and
retune. If you get streamers that are simultaneously breaking out in
more than one place, increase the radius of curvature of the toroid a
bit more. 

Good Luck, and safe coilin' to you Pete!

-- Bert --

Tesla List wrote:
> 
> ----------
> From:  Pete [SMTP:casius-at-cyberserv.co.za]
> Sent:  Tuesday, August 18, 1998 4:04 PM
> To:  tesla-at-pupman-dot-com
> Subject:  Please Help
> 
> Hi John Freau and all,
> 
> John, thanks for the welcome back. Was away from home and rather busy at
> work with a project. It's nice to be back on the list. Thanks also for
> your comments re my NST coil. I think I have asked most of the questions
> before but I seem to have great success with valves and get wimpy sparks
> with NST units.
> Let me start from scratch. My NST Tesla coil is as follows:-
> Two 12kv 30ma NST's in parrallel (total 60ma). The spark gap is directly
> accross the NST (8 x 1/2 x1" Cu tubes spaced 0.015"). A bank of
> capacitors in series (0.1uF x 8 = 0,0125UF at 50kV) comes off one side
> of the spark gap and ties to the primary inside turn. The primary is a
> 12 turn 30 degree inverted saucer wound with 1/4" copper tube spaced
> 1/4". The coil is tapped at turn 7 and returns to the other side of the
> spark gap. A 4" x 19" secondary  wound with 22 gauge copper wire sits in
> the centre of the primary. I calulate the frequency with toroid as
> +/-348kHz. The spacing between primary and secondary is 1". The bottom
> winding of the secondary is level with the 1st turn of the primary. The
> bottom of the secondary goes to an out side earth via a 1/4" copper
> stranded wire. The earth rod is 4 foot into the ground. The secondary
> has a 9" x 1.5" toroid made of ribbed PVC pipe and wrapped aluminium
> foil. A thin aluminium "plate" ( one of those disposable plates) sits
> neatly on top of the wrapped PVC tube to complete the toroid which I
> calulate at +/-10 pF. The toroid is 2" above the last winding of the
> secondary. There is no NST protection.
> Thats the setup. Even if I start tapping at turn 5 and go upto turn 8,
> the best spark is 12". What could be the problem?. By the way the
> capacitors are Plessy canned caps filled with visconol. There physical
> size is 3"x2.5"x1.75" for each cap.I get the feeling that the problem
> may be the caps I use.!!!!
> 
> Richard Craven,
> If you are still out there. How's that 5CX1500A tube coil of yours
> performing. I have had great results with my 5762 unit. The only problem
> is that I have run out out power for the beast. Just can't supply enough
> current. Had to settle for 650mm discharges for the moment. The 2 x 833A
> unit is less hungry for power and is more manageable.
> 
> Regards
> Pete Scully
> South Africa

P