Re: Questions about first Tesla coil

Subject:   Re: Questions about first Tesla coil
  Date:    Tue, 22 Apr 1997 07:13:11 -0700
  From:    "DR.RESONANCE" <DR.RESONANCE-at-next-wave-dot-net>
    To:    "Tesla List" <tesla-at-pupman-dot-com>

Hello Owen:

You might try a neon sign transformer instead of the 2N3055 ocsillator
driving a flyback xmfr.  This setup will only produce 1-2 ma of drive
current.  Usually you need around 30-60 ma of drive at 12 Kv which makes
neon unit a good start.  Sometimes if you get the right shop owner and
are a student he will donate a unit to you --- never hurts to ask!!

A good suggestion not to use a pole pig until you have built a few
units first.  Pole xmfrs are extremely dangerous and will fry you in an

You can obtain free details on a reasonable design by requesting the
Oscillator Design Guide" from Resonance Research Corp, E11870 Shadylane
Rd., Baraboo,  WI  53913.  Send a $3.00 priority mail stamp (no cash or


> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-poodle.pupman-dot-com
> Subject: Questions about first Tesla coil
> Date: Sunday,April 20,1997 10:35 PM
> Subject:  Questions about first Tesla coil
>   Date:   Sat, 19 Apr 1997 19:56:13 -0400
>   From:   "Owen Lawrence" <owen-at-iosphere-dot-net>
>     To:   <tesla-at-pupman-dot-com>
>         Hello, fellow Tesla coil builders!  I thought I'd finally
> introduce myself
> after enjoying the banter on this list for a few weeks now.  My name is
> Owen Lawrence and I live near Ottawa.  Like any beginner I'm bustin'
> with a
> million questions, so I'll pose a few of them now.
>         When I was in high school I built a coil but was never quite
> happy with
> the results.  However it was entirely my own design so I'm still proud
> of
> it.  I'll describe what I can remember of it and you can tell me how I
> can
> do better the next time.  I've always had this dream of doing it over
> again
> and getting it right, so here goes.  The primary transformer was a small
> (brand new) ignition coil.  Starting with six volts DC I created pulses
> using a relay wired to vibrate.  My four capacitors wired in parallel
> were
> made of approximately one square foot of aluminum foil glued to each
> side
> of a slightly larger sheet of 1/16" plexiglass.  Each capacitor was
> spaced
> an inch or two from the other.  By my calculations at the time I recall
> assuming they were 50pF each, so 200pF in total.
>         My spark gap was made from two small bolts.  I filed off the
> threads near
> the end of one of them to make it round, and sparked to the head of the
> other bolt.  With a nut on the threads and a wire attached to the nut I
> had
> an adjustable spark gap.  Next, the primary winding was a cylinder of 14
> guage bare copper wire, maybe a dozen turns at one foot diameter, height
> of
> about 8" or 9" inches in total.  In the middle of this winding was my
> secondary, which was about (and I'm really guessing here since I never
> did
> count, even back then) 800 turns of 32 guage enamelled wire on a 2" PVC
> pipe about 18" long, terminated with a 1/4" stove bolt.  I don't
> remember
> at all how all of these parts were wired together.  Does it really
> matter?
>         In the end I was able to get sparks maybe 2" long.  I could draw
> multiple
> fine threads of sparks from anywhere along the secondary by holding my
> finger near it.  I had hoped for much longer sparks.  Now I can see many
> ways this coil could have been improved but it has been dismantled for
> nearly two decades and I just want to learn what I can from it.  I know
> it
> was functioning as a Tesla coil because I borrowed an oscilloscope and
> measured a frequency of roughly 32MHz with the typical damped envelope. 
> You can't belive how excited I was in the middle of the night when I
> first
> applied power.  Well, maybe you can.
>         So here's my question:  NOW it seems to me that 32MHz is much
> too high a
> frequency for this setup.  Is it the length of the secondary winding
> that
> really dictates the best frequency for a Tesla coil (assuming no
> capacitance, that is)?  I've tried out some of the formulas I've found
> in
> the archives and a more likely frequency seems to be in the
> neighbourhood
> of 2MHz.  Is it possible my coil was resonating at a much higher
> harmonic? 
> If so, could I have improved perfomance by adding capacitance to the
> tank
> circuit to lower the ring freqency to the same wavelength as my
> secondary
> coil?  (Sorry if I get the terms mixed up; correct me where I'm wrong
> and
> I'll learn eventually)  If my assumptions are not correct, can you tell
> me
> how you think this coil was performing?  
>         I would like to build a new coil and would like to use an
> ignition coil (I
> actually have the original one!) for my primary step up transformer. 
> These
> things are limited in the amount of power they can output, so I was
> wondering what sort of spark length I should expect from a Tesla coil
> properly designed around this limitation.  If all goes well, I will use
> the
> experience to take the step up to a neon sign transformer and see where
> that leads.  I also have an old microwave oven in the garage with a
> blown
> transformer, whatever that means.  Can anything be done with this?  But
> I'm
> getting ahead of myself.
>         As far as my primary winding goes, the dimensions I chose were
> completely
> arbitrary.  It just seemed to look right so that's how I did it.  Would
> I
> have benefitted from a smaller diameter?  Many of the Tesla coil plans I
> see these days (in magazines or whatever) seem to have a tightly wound
> primary with a diameter only slightly larger than the secondary.  I
> never
> liked these because they always used insulated wire which severly limits
> the choice of where it can be tapped.  I can't remember exactly who said
> it, but since I've been devouring what I can find on the internet about
> Tesla coils I read somebody's remark that they preferred the shape of
> the
> field produced by a spiral coil over that of a helix.  But that's where
> it
> ended.  What's the real explanation here?
>         Another question:  I also own a high voltage power supply that I
> built
> from an Information Unlimited kit (30KVDC).  I bet some of you are
> famliar
> with it, yes?  Two 2N3055 transistors and a flyback transformer.  Is
> there
> any reason why this wouldn't be good for operation in a Tesla coil?  I
> would definitely want to protect the diodes in the high voltage
> rectifier,
> though, because they're expensive.  I'm not gone on having a spark every
> 1/60th or 1/120th of a second, so if I have to wait while a capacitor
> charges that's fine.  Whatever works best with the equipment at hand.
>         Finally, I've seen some of the suggestions for building high
> voltage
> capacitors.  One problem mentioned was that for rolled capacitors once a
> certain length is exceeded inductance starts to become a problem. 
> Couldn't
> this be reduced by tapping off each plate along its length?  When it's
> all
> rolled up the tabs from each plate could all be joined together so you'd
> be
> drawing off charge from the side of the plate rather than the end. 
> You'd
> end up with terminals at each end of the capacitor.  Excuse the artwork:
>     ___|______|______|______|______|______|_______|______|______|__
>     |  +    +   +                                                 |
>     ---------------------------------------------------------------
> (dialectric inbetween)
>     ________________________________________________________________
>     |   -   -      -                                               |
>     --|-------|-------|------|------|-----|-----|----|-------|------
>     roll it up:  -------------------------------->
>           | +
>         /   \
>         ||||| 
>         -----
>         |   |
>         _____
>         ||||| 
>         \   /
>           | -
>         I have other questions (like, I still don't understand
> quenching, how much
> does a pole pig cost, and why isn't there a tesla builders' usenet news
> group) but these are the ones that have been nagging at me.  Hopefully I
> won't be the only one that would benefit from answers to any of these
> questions.  If you prefer to refer me to resources rather than answer
> questions directly, that's fine.  Any response will be much appreciated. 
> I'm very excited to have found such a cool bunch of people.  I've
> already
> got several offices of people oooh-ing and ahhhh-ing over your pictures
> of
> operating Tesla coils I've downloaded (my wife is the only holdout :)).
> Thanks a million and I'll talk to you later!
>   - Owen -