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Re: Tesla Coil Questions

Hello Josh,

> Hello, I have a few questions here:
> 
>   I have a 6" coil, 888 turns.  It has a toroid, aprox 20" x 4" (it's a
> little on the eliptical side, is that a problem?

It should be ok, even eliptical.

>  I know this toroid
> lowers the frequenency, and I'm looking to build the receiving coil.
> What length should I start with on the receiving coil?  I don't know how
> much lower the frequency is.  Any advice on tuning the receiver?

I'm afraid your going to need a frequency counter, occiliscope. etc.  You can
try doing it by calculation, but it will only get you in the ballpark.  There
are plenty of people here that can help you with these experiemnts.

> What do people here use to spin their PVC pipe's when applying
> varnish?

Lathes work well, or some other device that will support the secondary
horizontally while it spins slowly.  You want to use polyurethane, not
varnish, as it is a better choice for a lot of reasons.

>   What makes a good counterpoise?

Large piece(s) of sheet metal supported parallel to a cement floor by
insulators several inches from the surface.

>   Is the light coming from the spark gap hazardous to look at?

OF COURSE!  It is like a welder's arc.  Loaded with UV.  It will burn
your retinas.

>   I will be powering this coil (hasn't been completed yet) with a used
> neon sign transformer, 15kv, 60ma.  I was thinking it may be worth it to
> bring the voltage up slowly, rather than turning it on at once?  If so,
> is this something I should look into?  If it is, how do I do it?  I
> could easily do it with a large transistor and a pot, but I've been told
> solid-state stuff won't work well, especially near the transmitter.

Most of us use a variac to bring the voltage up gradually, instead of just
slamming full voltage into the transformer by throwing a switch.  It is much
easier on the components to bring the voltage up gently.

>   If you are building a transmitting coil, is RFI good?

Sorry, you lost me here.  If you mean Radio Frequency Interference (RFI), then
it is both good and bad.  If you are building a transmitting coil, then you
want the coil to transmit, ie - send out RFI.  But that can bring the FCC into
the picture.  And you don't want that.  Building a transmitting coil will
interfere with TV and Radio reception.  It is most illegal to do so.  It will
require that you conduct these experiments inside of a Faraday cage.  That
brings us to your next question.

>   What exactly is a faraday cage, and how is it made?  What are it's
> affects, especially relating to the transmission of power.  Can we
> transmit power with a faraday cage?

A faraday cage is a box of metal foil or mesh that is grounded to an RF ground.
If the RF producing device is inside the Faraday cage, the RF can't get out.  If
you are trying to protect a device from RF, you place it inside of a farady cage.
Either way, RF can't get through the "walls" of the cage.  For RF frequencies of
Tesla coil operation, chicken wire should work out well.  Aluminum foil would work
very well too if you are gluing it to a wall.  The metal "cage" must then be
grounded by connecting it to an RF ground.  If you are purposely building a
transmitting coil (read not breaking out sparks), then you will need to build
a cage around your entire operation.  Its not a fun task, but it will be
necessary to stay legal.

Scott Myers