QRZ! Ham Radio 1/QRZ Ham Radio Callsign Database - December 1993.iso/arrl/tesla

Text File | 1993-11-21 | 8.4 KB | 164 lines

Tesla coil information

Newsgroups: rec.radio.amateur.misc
From: [e-mail] (Paul Prescott)
Subject: Re: Telsa Coils

The best single source for information about Nikola Tesla, Tesla coils, and
similar apparatus is:

Lindsay Publications, Inc.
P.O. Box 12
Bradley, IL 60915-0012

Lindsay's offers primarily reprints of books and other information concerning
technology and techniques no longer in general use.

Recently I noticed the book "Inventions, Researches, and Writings of Nikola
Tesla" by Thomas Commerford Martin at a local bookstore.  Lindsay's offers
this book, but the one at the store was published by someone else, so this
book is currently available from two publishers.  Note: this book was
originally published in 1894 and deals mostly with Tesla's work with
polyphase currents and his lectures and demonstrations up to that time.
There is some information on his early work with "Tesla coils", but he was
actually just beginning his more famous work in this area at the time.
(Tesla's Colorado Springs experiments took place in 1899-1900.)

Regarding the specific questions on Tesla coil construction:  There are a
number of factors that need to be taken into account to get the best
performance (longest sparks).  One of them, the "Q", has already been
mentioned.  Basic rule of thumb is you want the length of the secondary
coil to be 2 to 2-1/2 times the diameter.  The next is a lot more tricky to
work out.  The length of wire used in the secondary should be equal to a
quarter wavelength of the resonant frequency.  This way you have a voltage
maximum at the free end of the coil.  From what I can tell (I've never
actually built a Tesla coil due to lack of money and facilities to do the
job right) this is no easy task.  You have to figure out where the secondary
is self-resonant, and tune the primary accordingly.  Alternately, or in
combination, you can tune the secondary by means of what Tesla called an
"elevated capacity", those globular capacitors one often sees on the end
of Tesla coil secondaries.  The disadvantage of the elevated capacity is
that it accumulates a charge.  This should make for shorter, less continuous,
less impressive discharges as opposed to a point.  Also, it's quite a bit
more dangerous due to the accumulated charge.

The most common alternative to the single spark gap in the primary, which
offers improved performance, is the rotary spark gap.  This is a set of
rotating contacts to increase the number of sparks and get more energy
into the system.  I have heard of the vacuum tube driven primary technique
but I haven't heard of many successes using it.  I'm figuring it's more
difficult because the tube oscillator must be tuned to the frequency of
the rest of the system, and this is usually not a known quantity until
after everything has been tuned up and operating.

I hope this information is of some use, and again I apologize for taking
up so much space on a (somewhat) unrelated topic.  Is there a Tesla
mailing list, or enough interest to start a newsgroup?  :)

Paul Prescott
N1AAC
[e-mail]

From: [e-mail] (Myron A. Calhoun)
Newsgroups: rec.radio.amateur.misc
Subject: Here is a TV flyback Tesla design

While cleaning up my workroom I found a schematic for a "TESLA COIL KIT"
sold (many years ago) by B & F Enterprises, 119 Foster Street, Peabody,
Massachusetts 01960 [phone]:
                                         O CAP terminal (VERY HIGH VOLTAGE!)
   +--------------------------------+    |
   |           +------------+       |    |
   |        | /             |       |    |
   |        |/              |       | || $         ******** DANGER *******
   +--------|               |  L2 = $ || $         *                     *
     2N3055 |\       L1 = 4 $   10  $ || $ L3      * I TAKE ABSOLUTELY   *
            | v       turns $  turns$ || $ is a    *                     *
              |             $       $ || $ fly-    *       ** NO **      *
              +---+      +--$    +--$ || $ back    *                     *
              |   |      |  $    |  $ || $ xfrmr   * RESPONSIBILITY FOR  *
            | ^   |      |  $    |  $ || $         * YOUR USE OR ABUSE   *
     2N3055 |/    |      |  $    |  $ || $         * OF THIS CIRCUIT!!!  *
   +--------|     |      |  |    |  $ || $         *                     *
   |        |\    |      |  |    |  | || $         ******** DANGER *******
   |        | \   |      |  |    |  |    |
   |           +--|------|--+    |  |    +------o 1  8  -  5  Pin connections
   +--------------|------|-------|--+    +-----o  8  7  5  4  to the following
                  |      |       |       +----o   5  6  6  2  flyback
                  |      |       |       +---o    7  4  8  1  transformers:
                  |      |       |           |    |  |  |  +-- 738192
                  +------|-------|-----------|    |  |  +----- 32-10008-4
                  |27 ohm|240 ohm|           |    |  +-------- 32-10014-1
                  +--R1--+---R2--+           |    +----------- 32-8859
                  |              |         -----
                  |              |         /////
                  -   12 volts   +

Quoting from the instructions:

  "WE TAKE NO RESPONSIBILITY FOR YOUR ACTIONS!!!

   The new windings must be added to the flyback transformer to allow
   adequate transistor drive capability.  These windings are hand wound
   on the bottom leg of the ferrite core where the original filament
   winding was located.  Remove and discard the original filament winding.
   In its place, wind first a ten turn, center-tapped, winding using
   approximately 30 inches of #20 or larger hookup wire.  This is easily
   accomplished by winding five turns at one end of the core and then
   twisting a loop in the free end before adding the second five turns.
   The complete ten-turn winding should then be held in place with a turn
   or two of electrical tape with the two ends and the center loop all
   protruding.  Connection can be made to the center loop when the
   insulation has been carefully removed.  If it becomes necessary to cut
   the center loop, be sure that the two ends are scraped and joined to
   form a mechanical as well as an electrical center-tap to the winding.
   [L2 in my drawing]

  "The second winding should be wound directly on top of the first but
   it should only have a total of four turns--two each side of the
   center-tap.  Again, wind two turns of #20 or larger hookup wire, pull
   and twist a center loop, and wind the other two turns.  Tape this
   winding in place on top of the first.  Do not let the center taps of
   two windings touch each other but they should not be more than one
   quarter of an inch apart.  [L1 in my drawing]

  "Wire the modified transformer to the transistors and the bias circuit
   resistors as indicated on the schematic circuit diagram.  Be sure to
   mount the transistors on a suitable heat sink with the insulating
   hardware provided to protect them from over heating.  Since the
   collector connection of these transistors is made to the case, it is
   necessary to keep them electrically isolated from one another and
   from the heat sink and insulators are provided to allow this.  Heat
   sink area of approximately 25 square inches should be adequate.  If,
   however, the power transistors become too hot to hold a finger on,
   more heat sink area should be provided.  Heat sink material of one-
   eighth inch aluminum is desirable.

  "Note:  If Oscillation does not start Immediately Interchange the two
          Transistor Base connections [capitalization as in original!]

  "CAUTION:  LETHAL VOLTAGES ARE INHERENT IN THIS DEVICE.  EXTREME
   CAUTION MUST BE EXERCISED TO KEEP THE FULL OUTPUT OF THIS DEVICE
   FROM BEING APPLIED LIMB-TO-LIMB OF ANY LIVING ANIMAL.  SEVERE BURNS
   OR DEATH MAY RESULT FROM CONTACT WITH THE FULL OUTPUT..."

There were other instructions about how much damage might accrue to a
human if contact were made to the high-voltage output, so BE CAREFUL!

I used one-half watt resistors for R1 (27 ohms) and R2 (240 ohms) and
got a nice Jacob's ladder effect.  It also wiped out most of the
computer terminals in the entire building, so I couldn't run it very
much!  I later tried 18 volts and one resistor zapped immediately!

The members and HQ staff would like to thank the following people for
their contributions to this information file:

N1AAC, W0PBV

Send any additional information or changes to [e-mail].

73 from ARRL HQ.