Re: First attempt to build a smallish coil

["Gregory R. Hunter" <ghunter-at-accucomm-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Hi Henry,

Welcome.  You've taken your first steps in a useless yet thoroughly
exasperating hobby.  My comments are interspersed with your questions below.

At 12:57 PM 09/10/2000 -0600, you wrote:
>Original poster: Hhchicken1-at-aol-dot-com 
>
>Hi! I've decided to build a fairly small tesla coil - the secondary I've 
>built (very quickly) is wrapped around a cylinder 9cm high, with a 3cm 
>diameter. It is wound with about 200 turns of single core wire (probably too 
>thick, and not enough turns, right?)

Right.  You need some enamel insulated copper magnet wire.  For the tiny
secondary you are winding, I suggest small stuff, such as 30 SWG.  You can
buy small (500g to 1kg) spools of magnet wire from the Scientific Wire
Company just north of London.  They are in the Yellow pages.  Phone them
and they will express ship it anywhere in the UK.  If you live near London,
you can save yourself a few pounds by buying it over the counter.

>I'm going to make a primary with thinnish copper pipe coiled in a saucer 
>shape. Is this right? :)

Yes.

>I'm going to use a salt-water glass bottle cap, do I only need one or should 
>I wire several in series or parallel?

You need to know the output of your power supply before you can make a
guess about the capacitor size.  I suggest one of the Tesla coil design
programs available on the internet to calculate capacitor size for you.  

Saltwater caps are usually paralleled to increase capacitance.  I can't
think of any reason to place them in series.

>My spark gap is made of 4 pieces of copper pipe arranged in a row with a 5mm 
>gap between each. Is this wide enough?

Again, gap spacing depends on the voltage of your power supply.

>I'm not sure what sort of transformer to use. At the moment I can use either:
>a. A single MOT. What is ballast and would I need it?

A single MOT is not a viable option.  It produces too much current and too
little voltage.  It is also major overkill for the very small coil you are
contemplating.

>b. Two 240v-9v transformers wired in series and operated from 20VAC - 
>theoretically giving around 12kV, but at such low current I don't think it's 
>feasible.
>
>I don't yet have an NST, they are quite hard to come by in England.

For a first coil, consider using a car ignition coil pulsed from the mains
with a standard lamp dimmer switch available from any DIY store.  Limit the
current with a 1 or 2uF motor start capacitor in series with the dimmer.
This is a very cheap power supply suitable for a small coil.  I used an
ignition coil to power my first Tesla coil many years ago, and it worked
pretty well.

>
>Thanks for your help!
>Henry 
>
Best Regards,

Greg
www.angelfire-dot-com/ga3/tesla