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First light, and a poor performance




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From:  Gary Lau  24-Aug-1998 0807 [SMTP:lau-at-hdecad.ENET.dec-dot-com]
Sent:  Monday, August 24, 1998 7:33 AM
To:  tesla-at-pupman-dot-com
Subject:  Re: First light, and a poor performance

>From:  Steve Rodway [SMTP:Legion-at-legion-elec.demon.co.uk]
>
>Hi all,
>    Just fired up my new TC for the first time tonight, and
>unfortunately the output fell somewhat short of what I was expecting,
>I'd be very grateful if anyone could make a few suggestions about how to
>improve it.
>    The system specs are as follows.
>    Power supply, 11 kV (rms) polepig with resistive ballast made of 4Kw
>of heating elements filter consists of 2x20mH inductors and a 1.7nF
>bypass cap. Main tank capacitor is 7.42nF and the primary coil is a 30
>degree inverse conical with 12 turns of 1 mm wire 7 mm apart. The
>primary is spaced 20 mm from the secondary and the bottom turn of each
>coil line up. The gap is 6x0.5mm tungsten carbide static gaps.
>    The secondary is 4" dia and wound to 16.5" with 0.56mm enameled
>wire, there are around 660 turns giving an inductance of 11.4mH and a
>capacitance of around 8pF.
>
>    The system was run at first with no top load, tuning was around turn
>6 and the maximum arc length to a grounded rod was 8", with a 4"
>spherical top load then the arcs reached 11".  When the system was run
>for any length of time, the nickel coating on the top load was etched
>through, and when the plastic underneath was burnt then the arc length
>decreased dramatically. Also it was found after a short while that the
>acrylic support structure of the gap had melted.
>
>    I am planning tomorrow to build a much better gap that can take the
>heat for longer and a finite element array toroid 14"x3". that should
>bring the system to 1/4 wave operation, and, I hope increase the output
>because from looking at other's coils, 11" from 4Kw seems very poor.
>If anyone else has any other suggestions for improving the system, I'd
>really like to hear them.
>
>**********************************************************************
>*Stephen Rodway             Legion-at-Bigfoot-dot-com *  Support your local *
>*Tel. 0973 480 692                             *     coroner....     *
>*For Email use PGP where possible.             *    Die strangely!   *
>*http://www.legion-elec.demon.co.uk/index.htm  *                     *
>**********************************************************************

Hi Stephen:

My thoughts:
1) Use of 1mm wire for primary is too small, copper tubing would be much
   better.
2) Static gap of 6x0.5mm (3mm total) is too small.  Since I use 9+mm with
   a 15KV NST you should be able to go to at least 6mm.
3) You didn't mention anything about airflow over your gaps.  Quenching
   will be nonexistant without forced airflow, and at the power levels
   you're operating at, difficult even with massive airflow.
4) Don't waste your time even thinking about operating without a topload.
   A 4" sphere isn't much better.  Even your proposed (finite element array?)
   3x14" toroid is too small to extract good performance from a pig.

Regards, Gary Lau
Waltham, MA USA