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Re: [TCML] first coil help

Hi Thomas,

To answer your first inquiry about the RF ground. You will find
that the general consensus of this list's think tank is to keep the
RF ground seperate from the mains ground to keep those nasty
RF transients of up to several thousand volts potential off of your
mains grouns and from finding their way back to any of the sen-
sitive electronics that happen to share your home's electrical
wiring with your coil project. Also, you can get nasty little RF
shock/burns when you touch the grounded control panel if
the mains grounded control panel is also wired to the RF ground.

As far as to the reason for your coil's dismal spark length per-
formance, the only component that I can think of that you did not
so much as mention is your spark gap. If the spark gap isn't set
right or isn't up to the task of properly cooling and quenching,
then your coil's output will likely also be substandard. If you
could give us a description of your spark gpa setup, this may "tell
the tale".

David Rieben

----- Original Message ----- From: "Ryckmans, Thomas" <Thomas.Ryckmans@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Thursday, March 20, 2008 9:43 AM
Subject: [TCML] first coil help


I am building my first Tesla coil, but having issues - sparks are
pathetic - about 1 cm from topload to a grounded object. Help is much
I am adding the same document as a Word attachement, in case the pics
don't make it. <<tesla.doc>>
First of all here is a picture of the thing on my kitchen table; scale
is provided by the yellow yardstick sitting on the primary (21 cm). In
the background there is a crate of the best beer in the world -

My first problem is that I find books and internet references on "RF
ground" a bit confusing. Several books (e.g electronic gadgets for the
evil genius, gadgeteer's goldmine) show a RF ground connected to the
mains ground as here (evil genius):

Other references state that the RF ground should be distinct from the
mains ground, to avoid frying electronic equipment etc.
Unfortunately I live in an apartment, so I would find it difficult to
drive an iron rod into the ground to create my own RF ground...
What would you recommend?

I am using a 6kV 50 mA NST to power

Here are some values for the coil; the calculated values are provided by

Primary is
Salt water bottle caps, 24 bottles for a total of 10 nF (measured)
Copper tubing (8 mm) with inside diameter 189 mm, spacing 25 mm
Measured values are
4 turns 1uH
5 turns 5 uH
6 turns 9 uH
7 turns 14 uH

Secondary is using a 130 mm (diameter) black tube, 320 mm high, with
(about) 14 turns/cm hence (about) 450 turns.

Measured value for the secondary coil is 3.53 mH

Calculated value for the top load is 7.3 pF and self capacitance of the
coil (calc) 5 pF assuming spherical top load with R=65 mm. In reality
the top load is cylindrical and I expect its capacitance to be a bit

This gives me a calculated resonance frequency of 767 kHz.
Using a signal generator with a LED indicating max current I get a
maximum current at 833 kHz - not too far away from calculated values.
Using a signal generator and an oscilloscope I get a resonance value at
909 kHz.

With my primary's capacitor at 10 nF I would need my primary inductance
around 3.5 uH to give a similar resonance frequency of about 850 kHz -
this turns out to be just between 4 and 5 turns of the primary coil.

Using the signal generator at 833 kHz and the oscilloscope, I get a
maximum voltage value for the primary coil+cap in parallel at around 3.5
turns - again, not too bad.

So far, so good. However when firing the coil, I get pathetich sparks
(about 1 cm long) between the top load and a (insulated) screwdriver I
hold above it.
What am I doing wrong?
I am using this configuration:

I tried the other configuration (cap and primary in series, below) I get
the same kind of results... which configuration would you recommend? The
series one (below) is said to offer more protection to the NST
apparently - I will add a Terry filter soon anyway.

Many thanks for your comments!


Thomas Ryckmans
P Pfizer Discovery Chemistry
Office 500.1.177A Lab 500.1.109
Global Research and Development ipc 351
Sandwich Kent CT13 9NJ
Phone +44 1304 643 735 Fax +44 1304 651 817
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