Jumping in with both feet?

From:  D.C. Cox [SMTP:DR.RESONANCE-at-next-wave-dot-net]
Sent:  Wednesday, January 28, 1998 11:56 AM
To:  Tesla List
Subject:  Re: Jumping in with both feet?

to: Steve

With a .02 or .03 MFD capacitor it should easily produce 48-56 inch
discharges.  One problem -- you are overcoupled.  Your primary should be in
a flat expanding spiral for the primary not 2/3 the way up the sec coil. 
This will also lead to flashovers from primary to sec coil which may damage
the magnet wire.  You may also want to switch to a larger top electrode
such as a 20 x 5 inch toroid for better electrostatic control and higher
output potential.  Drive current necessary is 120-150 ma at 10-12 kV for
this type of performance.


> From: Tesla List <tesla-at-pupman-dot-com>
> To: 'Tesla List' <tesla-at-pupman-dot-com>
> Subject: Jumping in with both feet?
> Date: Tuesday, January 27, 1998 10:57 PM
> ----------
> From:  SBJohnston-at-aol-dot-com [SMTP:SBJohnston-at-aol-dot-com]
> Sent:  Tuesday, January 27, 1998 3:48 PM
> To:  tesla-at-pupman-dot-com
> Subject:  Jumping in with both feet?
> Hello, Tesla-listers!
> Please allow me to introduce myself:  Steve Johnston, in York,
>   I'm 34, with 21 years as a ham radio experimenter and 15 years as a
> Broadcast Engineer (so I'm not a newbie to high voltage/current RF
>  I've had a passing interest in Tesla coils for years, but never took the
> time to fully study the details and build a system.  Over the past week,
> however, my interest has intensified greatly as I was fortunate enough to
> come upon a nicely-crafted TC whose owner had died (hopefully his passing
> not related to TC experiments!).  
> This coil stands about 5 feet high not counting a top discharge terminal.
>   The primary is made of 11 turns of 3/8" Copper tubing, spread about 12"
> high and 26" in diameter.  The tubing is air-wound, held separated by
> (nylon?) spacers.  The secondary is wound with about #22 wire around a
> cylinder of 1/2" wide varnished wooden strips spaced about 1/2" apart. 
> consists of two sections in series, each 2' long, about 3 inches between
> two sections, for an overall winding length of 4'.  It is 16" in diameter
> with about 13 turns per inch.    The secondary sits about 2/3 of the way
> the primary -- perhaps by design to set the coupling between windings?
> There is a dome-shaped metal cover about 8 " tall and 6" in diameter that
> probably intended to be a top discharge terminal.   It could connect to
> center contact bolt on the top of the secondary with a short length of
> wire.
> The "exciter" (if that is an appropriate term?) is built into a metal
> and consists of a Variac driving a 15 KV 30 ma neon sign xfmr (half the
> winding is used, centertap to one end),  a small series inductor, and
> caps in parallel.  The caps are of unusual physical design (to me) but
> homemade -- the four together measure about 0.02 uF.  The spark gap is
> commercially-made with circular, D-shaped electrodes with cooling fins
>  -- the gap is easily adjusted.
> Any opinions as to the capabilities of this rig?  Would it be meaningful
> temporarily short the spark gap and attempt to grid-dip the primary tank
> see where it resonates?   Does the secondary self-resonate with
> capacitance?  To what spacing should I set the gap when I start testing? 

> Am I asking too many questions?  I guess I'm way too excited and eager to
> started...
> Thanks for any opinions and information!
> Steve Johnston
> sbjohnston-at-aol-dot-com