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Re: [TCML] first coil help

Hi Thomas,

Hey, could you give some other info?

The primary spacing (is that edge to edge or pitch which is center to center)?

Your secondary wire. Is it magnet wire or some other with heavy insulation?

Also, could not see your pics (would have liked to). Attachments don't make it (even Word documents). But Chip can put them on his pupman site in the List Images area (just contact him). Or, if you want, just send them to me and I can put them up at my site (email is "bartb@xxxxxxxxxxxxxxxx).

I have a feeling there's more going on here than spark gap. For one, the measured secondary inductance, frequency, etc.. does not equate out to a 14 turns/cm value at 450 turns (nor would the frequency unless there was considerable spacing as might be seen with insulations other than magnet wire, which is why I ask above about the wire). Something like 14 turns per cm of 450 turns would measure nearer to 5.5mH or near. Since your measuring 3.5mH, something's not right. I think you have some hefty wire on the coil and some tuning issues, but I can't be certain without some above info. Maybe you can simply measure the secondary bare wire diameter and total wire diameter for me? That would be helpful.

With your coil size, the RF ground is not the problem with sparks. However, in an apartment, you really don't want to connect RF to water pipes or anything like that, and you don't want to connect it to mains ground either (both are connected to your neighbors). So, a counterpoise is probably the best option in this case from a safety standpoint so that there is not a direct connection to your neighbors DVD player or to their bathtub.

Take care,

Ryckmans, Thomas wrote:
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
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