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Re: ground ring

In a message dated 6/28/00 7:03:27 AM Pacific Daylight Time, 
richardbarton-at-caving5.freeserve.co.uk writes:

> Can anyone throw light on my problem please.
>  I've just completed my 3rd coil.... the largest yet, with a 4-turn
>  small-bore copper tube primary, 1733 turn secondary of 
>  around 29" length, wound on grey ABS drainpipe of 3.75 O.D.
>  4-gap spark, with blower, and 3 neon TX= 12000V/90mA.
>  The cap is a beer-bottle/salt water type, 2.3 nF. 


( Chip, It's great to have the list back again, thanks for all your efforts
which are greatly appreciated !!!! )

With a secondary with that many turns, and a primary of such few
turns, you will need a huge capacitor to tune the coil.  I would say
that the coil is not tuned.  It is good to use a secondary that has
a lot of turns, but then the primary needs a lot of turns too to tune
it, (or a huge cap).  The reason I like to use a lot of secondary
turns is to permit me to use a lot of primary turns which increases
the primary surge impedance and reduces the gap losses.  If you
use a primary with few turns, and a huge cap, you lose that 
advantage though.

>  I'm a present
>  usingh an 18" foil-covered polystyrene sphere. Problem is,
>  I'm getting hardly any output, but with the sphere removed I'm
>  getting a thin blue spark of around 2" from the coil top to ground.

That's a huge topload, so even if all was correct, it may have problems
breaking out also the foil may have some sharp edges which will help
to permit breakout.  But in any case the coil is probably not tuned,
and the lack of tuning is preventing a good result.

>  I fitted a protective grounded ring around the top of the primary,
>  distance from it around 6" (First time I've used a top ring).
>  By the way, the primary is almost cylindrical, just a slight outward
>  incline to the supports. The safety ring is not a complete loop, but
>  its ends are about 1/4" apart. When I've been running the coil,
>  a big white continuous spark runs between these ends ! 

Yes, the ring should be grounded.  You don't really need the ring,
but you can leave it there as long as it doesn't arc like that.

John Freau

>  I presume this ring should be grounded ? Is the power going into
>  this ring and to earth, instead of going where it's supposed to ?
>  Everything is well insulated, and there's no other arcing going on.
>  Is this grounded ring worth bothering with, or should I remove it ?
>                   Richard Barton.