Re: perpendicular primary

To: tesla-at-pupman-dot-com
Subject: Re: perpendicular primary
From: "Dan Kline" <ntesla-at-ntesla.csd.sc.edu> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
Date: Tue, 21 Mar 2000 12:19:38 -0700
Approved: twftesla-at-uswest-dot-net
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme
>
>Original Poster: Parpp807-at-aol-dot-com 
>
>Hi Dan and all,
>I have a question--just for a change:
>Why is the flat spiral SOP for a TC primary? Has anyone experimented with a 
>solenoid
>of sufficient diameter to avoid the arcover problem?

I have a paper from somewhere around the turn of the century where a coil
is described in detail. The secondary is three feet long, and so is the
primary ;)
The primary is tri-filar wound of heavy solid copper wire. All the specs
are given except for the tank cap, I think. (I haven't re-read this for a
while)
The primary and secondary are held concentric, under oil. The outputs of
this bipolar coil are brought out in troughs of oil, each trough being five
feet long and 4 inches square. The wire is held in the center of the oil in
the trough. From the terminals, the lecturer claims that "torrents of
sparks 64 inches long" are emitted from the terminals. Interesting, eh? But
I can't find the reference anymore! I know it exists, because I made the
copy of the article myself! *sigh*

In researching Tesla coils, I found that all of the early plans (pre,
during, and post-depression era) called for helical primaries, and almost
all of the designs were bipolar. Kenneth Sweezy(sp?) was a confidant of
Tesla's at the time, and wrote a construction article himself. He calls for
a conical primary on a monopolar design. Except for a few tube-coil
designs, Sweezy's design was state of the art up until about 1975. Then
things began to change. Even on the list, although the "candlestick"
secondary had been abandoned in favor of better height/diameter ratios,
conical primaries were still considered best until about a year and a half
ago. 

My opinion is that the early designs were self-limiting as far as
power-processing was concerned. The materials available then were nothing
compared to what we have now. As coils have gotten more efficient, more
power can be processed, especially pulse power. If you look at primary
designs from the last 100 years, and let them morph in your mind to the
flat primary of today, and you can see that primary shape has change in
direct compensation of increased pulse power processing capability.

So to answer your question: "Flat spiral primaries help eliminate problems
caused by over-coupling and and the problem of processing excess power."
i.e. racing sparks and double-humping in the tuning curve. That doesn't
mean that a helix won't work...it will just have to very large :)

And as usual, these are just my *opinions* ;) I am *not* proposing natural
laws ;)

>I made a perpendicular primary for the 3.5 inch diam secondary on my 1/2 wave
>bipolar. It is a huge deadly spider web nearly 18 inches in diameter. I have 
>ten turns of
>3/16 Cu tubing with a 0.75 inch spacing. Well, that's what I tried to get.  
>:-)) I find a very
>sharp f res at 74 kHz and a very broad tuning with lateral adjustment along 
>the secondary.
>I guess the flat coil at the electrical center produces sort of an 
>ellipsoidal field. Is that good? That is why I ask the question on the flat 
>spiral use with a regular TC. Unlike the large solenoid, there is no arcing. 
>Perhaps this is a good clue to the 
>poor coupling.  Aside from the mechanical problems of safely supporting this 
>monster, I'm not overly impressed by the results compared to the performance 
>of a 6 inch diam -12 turn
>solenoid. I will try another flat coil wound to 0.50 spacing and a few more 
>turns to 
>increase the inductance.

Is there any reason you can't go to .25" edge-to-edge spacing, or are you
talking about .5 inches center-to-center?

>Does anyone have any ideas?
>
>Happy day,
>Ralph Zekelman

Dan