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Re: Off-axis primary inductance

On Sat, 28 Nov 1998 13:10:36 -0700 in the Tesla List
<Hollmike-at-aol-dot-com> wrote:

>>  Actually if you guys took a good look at the photos of Dr. Tesla's
>>  colorado spring coil you would see that he to used an off-axis 
>>  tunable inductor to fine tune his primary and secondary circuits...
 
>Alfred,
>I have seen this.  It just seems that no one today uses such a design 
>and almost always people try to minimize the inductance of the primary 
>circuit that is not actually coupled to the secondary.

Hi ya Mike, you right most people do try to minimize the primary
circuit's
inductance and with good reason: The operating principle of a Tesla coil
is such that in theory (remember this is only in theory) the voltage
output
is related to the primary voltage and the ratio of primary to secondary
inductance or it could be said that it is also related to the inverse
ratio
of the primary to secondary's capacitance. Thus ideally we want a coil
such
that the secondary has as much inductance as possible while having the
least amount of distributed capacitance and at the same time we should
strive for a primary circuit with as much capacitance as is practical
along
with as small an inductance as possible. Following these rules one should
get the highest possible voltage ratio for a given coil. Of course in the
real world things are NEVER that easy nor as straight forward.

>I was just applauding the idea of the tuning coil and will put one in my
tank
>circuit in my lastest coil :o)

And I think with good reason, the old master, Tesla himself, was a smart
cookie
and rarely did anything with out a deliberate purpose and his adding the
adjustable off axis inductance to help tune his coils was a darn good
idea.
On critically designed coils one finds that the slightest little movement
of the
primary tap throws the circuit in and out of tune, a smaller adjustable
inductance added in series makes fine tuning possible and the reward is
greater
output in response to this sharp tuning. Personally I have used
adjustable off axis
inductors in all but my first coil, and I found they are an excellent
addition.
Especially if you put them under mineral oil to prevent coronal leakage.

                               Alfred A. Skrocki
                          Alfred.Skrocki.Sr-at-JUNO-dot-com
                 Visit my Do-It-Yourself Aquarium WEB page at:
                  http://WWW.GeoCities-dot-com/CapeCanaveral/6251


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