The Turn Of The Century Electrotherapy Museum
(C) Jeff Behary 2007


In response to efficiency questions on the latest Tesla List postings...
My comments are interspaced below in "violet" ink...

From: "Tesla list" <>
To: <>
Sent: Saturday, June 16, 2007 11:36 AM
Subject: RE: [] conical secondary (fwd)

> ---------- Forwarded message ----------
> Date: Sat, 16 Jun 2007 11:47:04 -0400
> To: Tesla list <>
> Subject: RE: [] conical secondary (fwd)

> Sorry, but I've yet to see evidence of any functional advantage to using
> conical (or pancake) secondary coils vs. cylindrical ones.
> That Tesla used conical coils doesn't make it best.  He used cotton
> covered wire, beeswax, and salt water caps, but I wouldn't count these
> as best practices.

Cotton Covered Wire:  Virtually all pioneers of Tesla technologies from the 1890s until the 1940s
(Nikola Tesla included) agreed that Magnet Wire is considered "useless" for making Tesla Coils to
a certain degree...

Any form of insulation when dealing with high frequencies provides a mechanical insulation more
than an electrical one.  This "mechanical" insulation is later normally embedded with shellac, wax, oil,
etc. in order to provide a maximum protection both electrically and mechanically...

Tesla stated in 1897 that he used quadruple cotton covered wire to insulate his Pancake Coils, and later
used normal magnet wire wound with a required thickness of string to achieve the proper distances in his coils.
Tesla Coil X-Ray pioneer T. B. Kinraide used silk-covered magnet wire that was covered EIGHT times in order to
insulate his coils properly.

Today we have rubber and PVC coated wire.  These work great for Cylindrical and Conical Tesla Coils,
no argument there, but for Pancake Coils they are useless.  The original cotton and silk covering allows
insulation to flow THROUGH the windings and saturate all interstices of the coil up to the wire itself.
 When plastic covered wire is used (even under vacuum impregnation) small voids and air pockets result from the
tension of turns next to each other.  Sections of the coil can become "vacuum-tight" as it were though still have air
trapped within these voids found between turns.  The result is a coil that works really well for a split second and
then pours out black smoke from within.

Salt Water Capacitors:  Tesla used these in Colorado Springs because he was using a 60,000 volt
transformer to charge his tank circuits.  At the enormous power levels that this system was operating at
(remember he blew the main transformer of the town early on) it was a remarkable arrangement.
He was working with 3 1/2 times the voltage of most pole pigs and power levels inaccessible to most Tesla

In his portable apparatus such as these below he was using simple tin foil and waxed paper.  He proved that even
though the dielectric was in some cases only a few thousandths of an inch, complete vacuum impregnation allowed
the condensers to be operated continuously.  Several of these table top coils were operating at a kilowatt or more.
Further he found that the heat normally developed in the primary winding of a Tesla Coil was transferred to the
tin foil of the condenser and dissipated due to the large surface area of the later. 

[We've seen collectors with antique coils that have operated fine for a century replace the caps with modern pulse caps
(mfd equivalents but less surface area of metal) only to find their machines burning out mysteriously afterward...]

> Yes the coupling will be higher if the secondary base is wider, but one
> simply has to move the primary closer to achieve whatever coupling is
> desired.

In practice this is different.  In the early days (1896-97) people tried to make commercial X-Ray coils that used Cylindrical coils
instead of Pancake Coils.  A classic example can be seen here:

In order to insulate the coil properly once this coupling was achieved, the whole coil had to be immersed in oil - as the Primary winding
was made along the entire length of the secondary well within spark-over distances.  A good book on this topic was:
"The Tesla High Frequency Coil - Its Construction And Uses" by George F. Haller and Elmer Tiling Cunningham available at PV Scientific.
This concept works well, but is a horrible mess.  Five gallons of paraffin oil (kerosene) or linseed oil can be a bit of a fire hazard too, especially
near sparks!

> Why would corona losses be reduced with a conical secondary?  With a
> toroid atop a cylindrical secondary, I see no corona.

In Pancake and Conical Coils, as the voltage increases toward the center or top of the coil, the resistance decreases.  This removes the
stresses normally found at the tops of cylindrical coils (regardless of top load capacity).

> Claims that conical (or pancake) secondaries are more efficient appear
> to be lacking evidence.  Jeff Behary's site (correct URL is
> is richly decorated with photos of
> non-cylindrical secondary coils, but there are precious few words
> describing the rest of the coil components by which to judge just how
> efficient the coil might actually be, and nothing actually making a fair
> comparison.  Making a coil simply produce photogenic sparks does not
> demonstrate superior efficiency.

Whatever information is lacking on my website can be obtained by asking.  There are no secrets here, simply observations made from the
past.  We still have over 2,000 xeroxed articles and 6,000 blueprints that have not yet made it to the [currently] 56,180 file website.

While the machines I built were crudely  made using trial, error, and intuition instead of complicated formulas, they never cease to interest and amaze
our guests.  Several people have commented that their interest in Tesla Coils has been for 50 years or more and some of the "primitive" antique
and reproduction devices we have here have "astonished them beyond words".   Many have commented that they have never seen the likes
of these coils their entire lives in studying the subject, and most have also admitted to never believing the older technologies were as valid as
some of our descriptions might imply until they witnessed them in person.

The components used in all of the coils I make are fairly simple.

12" x 24" x 4.75" high.  45 pounds.
Reproduction "Kilowatt" Kinraide Coil
1000 watt 2000V Microwave Oven Transformer
Capacitor:  Oil-filled Sangamo .1 MFD @ 4000 WVDC
Spark Gap:  4-series, 1/2" Diameter Tungsten with Aluminum Heat Sinks
Pancake Coils:  9" Diameter
Primaries:  2 1/2 turns 1/2" copper ribbon
Secondaries:  300 turns 31 AWG magnet wire
Insulation:  Paraffin Wax dissolved in Paraffin Oil
Input power:  110V @ 15A
1500 watts consumed.  Discharge seen with the eye is as seen above, approx. 8" in length point to ball.

10.5" x 25" x 4.5"
35 pounds.
Rotary Spark Gap Pancake Coil
 3500V 30mA  Neon Transformer
(3) Sangamo 2000V .1 MFD oil-filled capacitors in series
1 Rotary Spark Gap, approx. 3600 BPS.  60 teeth wheel, non-synchronous 1800 RPM motor, two adjustable 1/8" tungsten rods for spark gap.
105 watts consumed.  Discharge is 6 - 8" in length depending on the spark gap adjustment.  It can be extended to 9" but creeping sparks
start to appear on the fiber top at the base of the dischargers.

In Jamaica Plain MA my wife and I found the remains of Tesla Coil pioneer T. B. Kinraide.  These remains included several
hundred glass plate negatives of electrical discharges made with Pancake Coils from 1897 - 1901.  Included also were the remains of 10
of the Tesla Coils Kinraide made and used to test various concepts and create the discharges.  They remained untouched for over a century
on a dirt-floor laboratory underground that survived being covered with rotting leaves, frost and freezing earth, and the heat of summer
in Boston for over 100 years.  The "primitive" wax and rosin mixtures used (despite being found covered in mold) were cleaned up and all coils
still function electrically.  Such a discovery can fuel a lifetime of experimentation. 

You are welcome to stop by and see these original pieces anytime, as is anyone from the Tesla list.  We also have two original Waltham Speedometers
patented by Tesla that still work, and also a wealth of early paperwork concerning these devices.  We also have an original Tesla stopper lamp and first
edition 1891 London lecture.

The primitive insulations used in this time period were not so primitive.  They were the results of earlier experiments 100 years before with Static Machines
and 50 years prior with the invention of the first induction coils.  (I've seen Franklin type static machines in Eastern Europe that STILL function!)
They were proven to take the test of time then, something that has continued to be proven today with their discovery.  Three condensers were also found in his
 lab that also function perfectly.  Most Tesla coils made in the 1920s and 30s still function today as well.  Yet trying to find a working Tesla Coil built from the 40s -
60s using "modern materials" is not so easy.  Very few were preserved, and those found are often in poor shape or are non-functioning. 

> > Date: Fri, 15 Jun 2007 19:25:06 -0700
> > From:
> > To: Tesla list <>
> > Cc:
> > Subject: Re: [] conical secondary (fwd)

> >
> >
> > It has been quite a while since I've written to the List.  This
> business about conical
> > secondary coils has caused me to now reply.  Finn, you are right.
> winding a conical
> > secondary coil (regardless of size) from the small diameter end to the
> large end
> > is the only way to go.  There are techniques that one can use to
> support the first
> > 10 or so windings to be held in place as you continue to wind.
> >
> > Why use a conical coil form?  It has nothing to do with "old classic
> designs".
> > Rather, it has to do with placing the greatest amount of the secondary
> coil
> > inductance in closer proxcimity to the primary coil.  Think about it.
> There is
> > another advantage to a conical secondary coil design.  That is,
> reduced
> > corona leakage stress at the top of the coil due to its shape (not
> withstanding
> > whatever "top load" electrode geometry you chose to use).
> >
> > Proof of how successful this secondary coil design can be?  Just look
> at the
> > Griffith Observatory coil on my web site at:  Also
> please
> > see the two one-to-one copies I've made of this coil: GPO-1 and GPO-2.
> > There is also a (mini) version of GPO-2 that is linked to my web site.
> > All these coils are up and running in a public venue setting.
> >
> > It interesting to note, that Tesla himself, in his first (medium size)
> resonator coil
> > at his 5th Ave. laboratory before it burned down, ( see the image of
> this coil
> > in the Beograd book "Tribute to Tesla"), and also his first secondary
> coil design
> > at Colorado Springs (in the book Colorado Springs Notes), were also
> conical
> > secondary coils.
> >
> > When it comes to design details of "what is the most efficient form of
> r.f.
> > resonator coil system"?  It goes like this:
> >
> > Least efficient (but most practical design to build): cylindrical
> secondary.
> > More efficient (but difficult to wind): conical secondary.
> > Most efficient (but the hardest to build): pancake secondary and
> primary.
> >
> > My friend and colleague Jeff Behary, has been making many new
> breakthroughs
> > in this last area of investigation.  Please see his web site at:
> >
> >
> > Best regards,
> > Bill Wysock.

My friend Bill Wysock and I share something in common aside from our love of Tesla.  We build apparatus that end up as conversations and debates of
Tesla enthusiasts around the world.  While many can criticize and theorize about these systems, the actual machines exist and are shown around the
country at lectures, demonstrations, etc.  Both of us also receive visitors from around the world to our homes from time to time that are making films,
documentaries, etc. about the work and life of Tesla.  If there wasn't truth in our words, or our work lacked a certain integrity we would not have these
opportunities, or rather our successes would have been short-lived.