Re: actual measurements & pictures of the TC in action


The idea of minimising corona is to protect the top turns of wire and the
former from being damaged. Heavy corona and plastics do not mix well, and
degradation may mean that the insulation of these top turns is compromised,
worsening breakdown problems. A grounded strike rail may also help by
evening out the e-field a bit more, but that's just a hunch. The spacing to
the toroid is really a matter of trial and error. Too low and you may get
these racing arcs (perhaps this is because it 'squashes' the e-field near
the top of the coil very close to the windings and the high voltage
gradient encourages the initiation of a downward spark), and too high and
the corona gets so bad that you have actual arcs off the top winding (not
good!). Just try to experiment - use little squares of wood or plastic, or
maybe even a few saucers or small plates to adjust the height. You may have
to alter the tune a bit if you raise or lower by more than a couple of
inches or so.

As for the splice, you have a toughie of a problem here. Since the wire is
already wound tightly on the former, you have no way of extending it to do
a simple overlap-splice. What I might suggest is pulling up the offending
turn and your present splice and cutting out that short damaged section.
Use a fine file to expose the bare copper and thin down the wire a bit. Put
a little strong glue on the former and lay the wire ends down again, making
sure the exposed copper faces outwards. Take a short length of tinned
copper wire (again try to thin the ends down a bit) and align it with the
gap so it overlaps the exposed ends. Very quickly and carefully solder this
to the ends, without damaging the insulation of adjacent turns. Put several
coats of varnish (or maybe some epoxy) over this until the bump is really
smooth. It's not ideal by any means but I just though about it and couldn't
imagine a more effective way without rewinding the bottom bit of the coil
completely. You could just try filing down the splice you already made a
bit and applying more varnish or epoxy, but I can't see how much of a bump
you have from the pics. 


From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com
Subject: Re: actual measurements & pictures of the TC in action
Date: 08 August 1999 13:43

Original Poster: Stan <sdarling-at-columbus.rr-dot-com> 

I suspected it was something along those lines.  Wish I had more
equipment :(  For now I guess I'll have to stick to using the
theoretical values of them.

Thank you. Not to sound stupid, but why is the corona at the top a big
deal?  I felt the secondary right after powering it off and it was
cold.  I need to find a better spacer--right now it's a plastic
enclousure box--I had to use something because without a spacer (which
meant about 2-3" between top turn and bottom of toroid) I was getting
heavy arcing down to the primary and other components.  And right now I
have only a safety gap and no strike rail since my RF ground is pretty

That is a hot-spot near the bottom.  Unfortunately my 6 mo old puppy
thought magnet wire would make a good chew toy and snapped one turn of
the secondary.  So that spot is where I spliced the wire.  Is there some
technique to minimize the spot?  I did my best to avoid sharp edges in
the splice.  Is it better to fold the splice part flat against the coil
or to stick it straight out?  It seemed to me the former was better
although I couldn't get it to be perfectly flat.