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RE: On the fly tuning of a TC



Original poster: "Lau, Gary by way of Terry Fritz <twftesla-at-uswest-dot-net>" <Gary.Lau-at-compaq-dot-com>

While not helpful towards the goal of the thread, I thought this is a good
time to recount a near-miss accident that happened to me while attempting
on-the-fly tuning.

I attempted to change primary tap points while running the coil so that I
could see which tap point gave the best sparks without having to power down
between iterations.  I fastened the tap wire to the end of a long piece of
PVC pipe, and with power on, dragged the tap wire across the primary.
Fierce sparks were drawn with each make or break of the connection, so I
quickly abandoned that idea.  I turned power off and reached for the loose
tap wire to securely connect it.  

ZAP!!!  I got quite a significant shock from the wire.  The capacitor is
normally discharged by the NST secondary when the primary circuit is
complete, but with the tap wire disconnected, this discharge mechanism is no
longer in effect.

I now have a permanently attached bleeder resistor across my cap, but the
point I wanted to make is, be very careful if you might create an open
circuit in your tank circuit.  You may create a charged cap without a
discharge path that may surprise you!

Gary Lau
Wellesley, MA USA


Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<FutureT-at-aol-dot-com>


Jason,

A good way to tune the primary is to build a metal roller that contacts
the primary copper tubing.  THen you make the whole primary so that
it can rotate around the center when driven by a gear motor.  As the
primary rotates to a new position, the roller will roll along the primary
copper tubing, and the tuning will change gradually.   As you can
see, the roller always contacts the tubing with this method, so there
will be no showers of sparks as the tuning changes.  The roller 
has to be build as an arm
mechanism that can move in or out as it follows the primary spiral.
The arm could be something like the arm on a record player (phonograph).

John Freau