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Re: bad coil

Subject:     Re: bad coil
      Date:  Thu, 29 May 1997 13:11:24 EDT
      From:  wb8jkr-at-juno-dot-com (Mark S Graalman)
        To: tesla-at-pupman-dot-com
References: 1


On Thu, 29 May 1997 07:44:20 -0500 Tesla List <tesla-at-pupman-dot-com> writes:
>Subject:  bad coil
>  Date:   Wed, 28 May 1997 01:29:20 -0400 (EDT)
>  From:  Damon Burke <damon-at-portal.stwing.upenn.edu>
>    To:  tesla-at-pupman-dot-com
>
>
>
>Hello.. I'm writing to you for help with my coil.  I read alot of 
>online
>material, searched through alot of web sites, and downloaded many
>programs
>so i could start building my tesla coil.  I finally finished it and
>despite my accurate construction (or what I considered rather 
>accurate)
>i
>find my coil arcing nearly 1/2" to a ground wire at the most.  I made 
>my
>primary tap moveable so i could attempt to tune the coil, but anywhere 
>i
>move it i get the same results.  Here is my coil specifications:
>
>I'm using a standard 120v 60hz input with a 15kv 30ma neon 
>transformer.
>I have gto wire running to all my components.  The entire set is built
>onto a wooden cart for portability.  Parallel to the transformer is my
>safety gap set to 3/4" (recommended by chip.)  Also parallel to these 
>is
>my static gap.  I'm using 8 gaps with somewhere between .01-.02 inch
>gaps
>(recommended by the teslac program.)  The gap was designed by placing 
>a
>strip of tin sheeting on a piece of wood and screwing it down in 9
>places.
>Between the screws i used a hacksaw to cdut a groove through the 
>metal.
>This gave me about 1/16 of an inch gaps.  I then turned the little
>strips
>of metal to close the gaps to their recommended gap sizes.
>
>Parallel to all of these of course is my cap/coil combination.  I have 
>a
>wooden box with three sheets of 1/4" thick window glass.  I have 
>10"x10"
>aluminum foil on each side of the glass.  Three of these are parallel 
>to
>each other bring me to just under .004 uf (the recommended capicatance
>for
>my coil is .0038 according to the teslac program.)  My primary coil is 
>8
>turns of 1/4" copper tubing with 1/4" spacing.  My first tap is on the
>very inside of the coil (soldered in place) and the other one is on a
>moveable mount somewhere between the 7th and 8th turns (as recommended
>by
>the teslac program.)  My secondary is 24 gauge wire on (can't 
>remember,
>either 3" or 4".. i believe 3") plexiglass tube.  The coil winding is
>12"
>high.  The bottom of the secondary lines up about the same height as 
>the
>primary (which is a flat spiral.)  
>
>The secondary has a wire that goes out the bottom to a ground rod sunk
>6'
>into the ground.  The top end  wire goes to a toroid made of 4" 
>diameter
>aluminum dryer duct material.  I didn't have alot of information on 
>the
>toroid so I used what i had and made a donut out of it.
>
>Here is a drawing of my coil design
>
>                                    _____
>+----+-----+---+---| |--+-------   (_____)
>|    |     |   |        |      o      8
>|    |     |   +---| |--+      o      8
>|    |     |   |        |      o      8
>           :   +---| |--+      o      8
>T          :                   o      8
>           :                   o      8
>|    |     |                   o      8
>|    |     |                   o      8
>|    |     |                   o      8
>+----+-----+--------------------      8
>                                      |
>^  Transformer      ^ Capicators     ---
>                                     \ /  <- ground
>     ^ Safety Gap
>  
>           ^ Static Gap
>
>
>I have placed a few small flourscent tubes near the coil, and they 
>glow
>quite well.  I can gring a ground wire close to a tube about a foot 
>form
>the primary and pull a 1/4" arc from it!  If i put the secondary near
>the
>primary i don't get any arc from it.
>
>If anyone out there has any ideas what i'm doing wrong please let me
>know.
>Also: what is involved in tuning a coil.. what items should i look to
>modify first?
>
>Thanks in advance for the help.
>
>Damon
>
>

    Damon, Teslac will recommend that you build the primary so that it
is
capable of resonanting about 100 Khz lower than the secondary
system to allow for experimentation with different top loads etc, and
the frequency requested by the primary design segment is the 
frequency of the secondary coil / terminal combination, not just the
calculated frequency of the secondary coil alone, this has to measured
or an accurate guess be made, but should be covered by the 100khz
lower frequency suggestion mentioned above. I have no idea just
how large your torus is, but I suspect because of its size your
secondary
system is in reality resonant much lower in frequency than
you primary circuit is capable of being tuned, just for the sake of
finding out, remove your terminal and try running tuning the coil again
and see if takes off.


                        Mark Graalman