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Re: Primary Size - 1/4", 3/8", 1/2" ? ? ? ?
Original poster: "D.C. Cox by way of Terry Fritz <twftesla-at-qwest-dot-net>" <resonance-at-jvlnet-dot-com>
I have to disagree with this statement.
We work a lot with 1/2, 5/8, 34/ and 1 inch copper tubing on various size
coils. It's easy to form primary coils but the trick is knowing how to do
The 60 ft. roll of perhaps 5/8 in OD (1/2 in ID) copper tubing comes in a
circle. Keep it in a circle and cut the box off of the tubing. Do NOT try
to straighten it out --- it work hardens. Trying to straighten the tubing
is a terrible mistake that most beginners make.
Mount your primary holders, ie delrin blocks on your primary base. Using a
copper tubing bender (local hardware store), form a 90 degree bend in the
copper tubing so it goes down into the base 8-12 in. (this hooks directly to
cap and saves a connection, ie, less resistive losses). Now you have the
copper tubing laying on top of the blocks. Hook the copper tubing into the
first primary holder notch.
You just carefully gently and very slightly start bending the copper tubing
1/2 to 3/4 turn AHEAD of your present location and slowly form it into the
radius of the primary holders. You keep going inserting the tubing into the
notches as your proceed and also continuing to form the tubing into a gentle
circle 3/4 turn ahead of each notch as you press the tubing into the
notches. Twist the entire roll of tubing sort of like SLOWLY turning a
steering wheel in a car. It can be slowly expanded or contracted slightly
as you continue to form the diameter to match your blocks. Start in the
center and go notch by notch outward as you go.
It's a bit awkward to describe this procedure but once you have done it ---
it's very easy. We hand form most of our tubing in this manner and do an
entire primary in 15-20 minutes max and do not use any tubing benders at all
except for the initial 90 degree bend.
At the very outer end use a tubing cutter to cut off. Be sure to sand this
down and insulate with electric tape or shrink tubing. This prevents the
sharp edge from forming corona up the coil and helps prevent electrostatic
problems leading to coil breakdown.
Also insulate the area where the innermost 90 degree bend goes down into the
primary base. You don't want losses into the wood or other material that
you are using as the upper primary support plate.
It's easy and should not be a difficult procedure. Just take your time and
use the "steering wheel" technique to keep expanding or slightly contracting
the entire copper tubing roll as you progress.
BTW, the blocks are machined across with a 90 degree ball nose cutter in a
milling machine. We usually make our blocks a standard 1 inch high x 3/4
inch wide to support the primary.
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
Sent: Sunday, September 15, 2002 3:01 PM
Subject: RE: Primary Size - 1/4", 3/8", 1/2" ? ? ? ?
> Original poster: "Dave Hartwick by way of Terry Fritz
> Just a note: My primary is made with 1/2" CU tubing and it is very
> to work with. I think quite a few guys have fired at 10 kW levels using
> 1/4" without problems.
> Dave H
> Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> Just a quick question . . .
> Just finished my 10" x 45" secondary coil and need to create my primary.
> Right now I'd like to size my primary for current duty (up to 5kW) but
> for the future up to 10kW power.
> Some people told me 1/4" was fine, but I think this is too small? What do
> you think? 1/4, 3/8 or 1/2" or bigger????