Re: Secondary Specs

        Re: Secondary Specs
        Wed, 16 Apr 1997 08:39:40 -0600 (MDT)
        Chip Atkinson <chip-at-XiG-dot-com>
        Tesla List <tesla-at-pupman-dot-com>

> Phil Chalk wrote:
> I am about to build my _first_ coil.  Initially it will be powered by a
> 12kV 30mA Neon, but I'd like to build a coil capable of coping with
> whatever other bigger transformers I might get lucky enough to come
> across for a while.

That's a good idea.  However, it has been my experience that a
has to cope with a coil, not the other way around.  I have powered a 3"
coil with about 120ma without any trouble.  

> So at this stage I'm thinking of a 10" diameter secondary, on some
> 'nice' plastic, not PVC.  I'd like to wind it with about #18 or even #16
> wire.  #18 gives about 34" winding length for 800 turns & about 42" for
> 1000 turns, close-wound.

Hold on there!  a 10" coil would be way cool, but I'd highly recommend
something smaller such as a 3" or 4" diameter coil.  

Building a TC takes a fair amount of learning and often money.  As the
size goes up, the cost does too.  If you start small, the mistakes you
make are relatively cheap.  If you blow a cap, its going to be less
expensive than if you blow a cap for a 10" coil.

The other problem is that a 12-30 transformer will be too small to power
the thing.  You'll have a difficult time getting much output.

My first coil was 8"  in diameter and I never got much out of it.  I
powered it with a 12-60 and later a 12-30 (Kv-mA) neon transformer.  The
results were disappointing by today's standards (6-8 inch sparks to
ground, no streamers).  It wasn't until my third coil that I got any
streamers at all.  This third coil was a 3" diameter coil that was made
closely to the specifications of a coil that Gary Legel of TCBA built. 

Granted I didn't have access to as much knowledge when I started, as you
do through the list.

Another consideration is where you go from 10".  If you start at 3" and
make a nice coil that runs well, show your friends and they are
etc., then you make another larger coil and repeat.  If you start at
you'll have to really improve the spark length the next time you show it
to re-impress people :-)

> I haven't given the primary much thought yet  - probably about 1/4" -
> 1/2" copper tube (What's the advantage of 'conical' primaries ?)

For a 3" coil, I'd go with 1/4", a 4" coil, 3/8", a 10" perhaps 1/2" or
3/4" (I don't know about the larger sizes as I have no experience and
don't remember the recommendations made by others)

> So I just wanted to draw on the pool of knowledge & experience here, &
> see what comments anyone has about my suggested dimensions, etc, before
> I go and spend the bucks!

You can save yourself a bunch of money if you do the following things:

1) Improvise -- keep your eyes open for things such as pipe scraps,
wire, pieces of plywood, etc. that you can get for free and save
having to buy.

2) Build it if you can, rather than buy it.  I'm a fan of the TCBOR
caps for example.  True the commercial caps are unmatched for
but the rolled caps are close, and much more economical.  (Note:  For
materials I have access to, it's most economical for me to buy the
materials for 3 rolled caps)

3) Shop the ham fests.  Keep your eyes open in particular for variacs,
wire, and anything else you may find useful.

> Anyone care to hazard a guess as to the performance of such a coil,
> properly tuned, etc, on the little neon ?? e.g. spark length ??

Guessing, you'd have trouble getting anything from a 10" coil powered by
12-30.  A 3" coil can give you streamers up to 16" long as I recall.

> Many Thanx,
> Phil Chalk.
> P.S.  Anyone know of a source of 'nice' aluminium (copper ?, whatever)
> torroids ?

You can build them yourself, and they look half decent.  I use flexible
aluminum ducting and some sort of disk in the center.  Here's my latest

0) I'm assuming that you know the size of the toroid you wish to make.

1) Get a disk of suitable material (I'm using wooden cable spool ends)

2) Make some blocks to lift the disk up so that the center line of the
edge of the disk is even with the centerline of the dryer ducting.

  Disk            /
---------------- /
               | |
               | |
 Centerline -->| |<-- Centerline of 
    of         | |    ducting
   disk        | \
----------------  \
########           \
########            \
########              \
########                 _________
Block of material

3) Place the materials on the floor, or some flat surface that's 
   big enough to rest the whole assembly on.

4) Fix the ducting to the disk somehow.  I'm using hot glue, which
is great for wood to metal.  For an aluminum disk, I'd use aluminum
solder, available at a welding store.

5) Coat the disk with foil or something conductive.  You also need
to allow for a connection between the ducting and the top of the

This technique should give you a planar toroid that looks fairly

First Corollary of Taber's Second Law:
        Machines that purterb people often get murdered.
               -- Pat Taber