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Re: Tunable Primary coil



At 02:25 PM 1/19/97 -0700, you wrote:
>Subscriber: nikki-at-fastlane-dot-net Sun Jan 19 14:05:29 1997
>Date: Sun, 19 Jan 1997 10:49:02 -0600 (CST)
>From: Bert Pool <nikki-at-fastlane-dot-net>
>To: tesla-at-pupman-dot-com
>Subject: Tunable Primary coil
>
>Just thought I'd give a quick update on the tunable primary I've been
>building for my large magnifier.
>
>It ended up being 29 inches in diameter.  Magnifiers typically use a
>cylinderical primary with a tightly coupled secondary inside, and this uses
>this same design.  Insulation between the two is usually very heavy poly
>steeting.
>
>All my primaries in the past have been roughly tuned by tapping the turns
>for approximate tune, then half or quarter turns for final tune - sound
>familiar?  In about 1976 I came up with a design for a primary that allows
>you to change the spacing between the turns to do precision tuning, even as
>the coil is running.  I built such a primary for a very large coil (primary
>was 9 feet in diameter) and the tuning worked beautifully.  This 29 inch
>primary is the only other primary that I've built using this technique.
>Because you have at least six vertical pipes which pvot in the center, and
>the fact that each place where the wire connects to an upright has to have a
>pivot as well amounts to drilling a lot of holes and making a lot of moving
>parts.
>
>I started out building an open frame out of 2 inch and 1.5 inch pvc pipe to
>form a cage-like structure upon which to wind the primary.  I found 12
>verticals to be too many, operation was stiff and mechanical resistance of
>the large coax wound on the form was excessive.  I reduced the number of
>uprights to six, and changed the pivot points on the 1.5 inch pvc from
>threaded pipe fittings to a simple plastic pin arrangement and now it works
>like it is supposed to.
>
>A friend and I will be measuring the amount of inductance shift the tuning
>arrangement provides later this Sunday.  We also are abount to insulate the
>secondary and hope to fire up this magnifier for the first time!
>
>I'll post the results of the measurements and whether we set any smoke free
>later.
>
>
>Bert Pool
>nikki-at-fastlane-dot-net
>
>
Let me quote something I found on magnifiers;

"This is just a big Tesla Coil having a third coil designed to oscillate in
resonance with the secondary. This "extra coil," as Tesla called it, can
oscillate just by being placed in the vicinity of a Tesla coil, but, in the
magnifying transmitter, its lower end is connected directly to the top of
the secondary. The primary and secondary are closely coupled."

There is nothing about a primary on the magnifier coil, can someone clear
this up for me, I had always wondered about this.

                                       Regards,
                                            Kevin Nardelle

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