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Re: Scopes Away! - mosfet

Tesla List wrote:
> 
> >From MALCOLM-at-directorate.wnp.ac.nzSun Sep 15 21:42:55 1996
> Date: Mon, 16 Sep 1996 08:03:42 +1200
> From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
> To: tesla-at-pupman-dot-com
> Subject: Re: Scopes Away! - mosfet
> 
> Hi guys,
>           I suspect my comments may have been misconstrued. 

Big snip
> 
> I'm not proposing to use MOSFETs at any real power. I am using them
> to replace the gap in some low power experiments to gain a better
> understanding of the limitations of systems and techniques currently
> in use. It is vital I have this knowledge for a future project that
> might indeed enable me to replace the gap with something more
> civilised (not thyratrons). I also want to see what the tradeoffs
> are between k and Qp.
>      In talking about established records, I was not denigrating
> Richard's 10X which is stunning by any standards, but length vs power.
> Perhaps one of you can confirm or refute that a 2-coil system run
> at the same k as the driver in a magnifier (same resonator) scores
> the same length for the same power input?
> 
> Thanks,
> Malcolm

Malcolm,

I would say that regardless of coil type, in expert hands, at a given coupling, a given power 
will only yield a given spark length in air. (period!!!)  I have always maintained that a 
doubling of input power by the most advanced coil expert (beyond 10KW) will only yield 25% more 
spark.  I further believe that even this ratio drops rapidly above 40KW!

The two coil system would have to be huge and massive to achieve plus ultra performance levels 
(like Greg Leyh's excellent coil-probably the biggest two coil system on the planet!)  The 
magnifier can take the same power and produce the same spark with greatly reduced size in the 
equipment.  There is no magic, just more or less volumetric efficiency.

Lower power 2 coil systems under 1KW can easily be made with spark lengths at the low end of 
this range of 8-20 feet/KW!!  At 1KW this falls to about 4 feet.  If one gets 6-8 feet of spark 
at 5,000 watts one is doing quite well, etc., etc, and so on.  This is why I hate the "X" 
number of feet per KW spec thrown out by the coilers.  It is so non-linear and so related to a 
coilers abilities, that any attempt at quantification is somewhat doomed to failure and some 
dork will prove it wrong by beating the limit.

Your efforts at low power work are commendable, but at these levels, it will seem that 100'/KW 
is obtainable when it is not!  I have always maintained that the relationship of the fall off of 
power with distance is related to a complex equation involving the inverse cube of the radius of 
the ionized sphere of air about the system.  I feel that the ionized air is a major causitive 
agent of the speark length and not solely the voltage.

I am attempting some crude H2 thyratron experiments (in the future) where the dwell time of the 
power pulse can be electronically controlled over a vast range.  The 5949 H2 thyratron can 
handle 6 million watts of peak power and about 600 amps of plate current at 16,000 volts.  This 
is almost as good as a medium sized coil's spark gap.  Tyhratrons, when on, are as close to a 
short as you can get!
The problem (there are always problems): H2 Thyratron tubes cost hundreds of dollars if ordered 
from the manufacturer.

Good luck in your experiments with the FETS and IGBTS, and we await the results of your work.


Richard Hull, TCBOR