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Re: Secondary additions and corona breakout

Subject:      Re: Secondary additions and corona breakout
       Date:  Tue, 20 May 1997 08:20:01 +1200
       From:  "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz>
Organization:  Wellington Polytechnic, NZ
         To:   tesla-at-pupman-dot-com


Hi Peter,

> > BTW, I'm currently making a version of one of Tesla's early 1/2-wave
> > lumped coils (a la the lecture to the AIEE) using modern materials
> > and a slightly different primary configuration. It also has a ferrite
> > rod for a core. I should be testing sometime this week.
> 
> Malcolm,
> 
> This sounds an interesting concept! Can you put bundles of ferrite rods
> inside a TC secondary (well insulated of course) to give you big
> inductance from a relatively small secondary?
> 
> Maybe there's hope for my 3.5" yet!!
> 
> Peter E.

Well you can. But I think you would risk losing a distributed 
resonator to breakdown, particularly near the top. Perhaps if 
the rods are totally potted with no airgaps inside the coil former.
    In the coil I am modelling mine after, Tesla had the primary 
wound under each of the lumped secondary coils. In my version, the 
primary is wound on its own bobbin in between the two windings. It 
has several windings of different numbers of turns so I can select a 
range of inductances for different primary L/C ratios. The rod is 
principally to provide a reasonable degree of coupling between 
primary and secondaries. It also increases the inductance of the 
secondary as a whole by a factor of 3 or so. I used a piece of PVC 
pipe into which the rod neatly fits and which in turn neatly fits 
inside the solder bobbins.
     The secondaries and primary are wound on separate solder reel 
bobbins. Each secondary consists of around 600 turns of thin PVC 
covered wire. The primary uses 1.2mm enamelled wire. There are three 
primary windings of around 10t, 20t and 30t, each separated by layers 
of Teflon and the entire primary is potted in bolt-barrier compound.
The whole thing is going to live in a perspex case and be totally 
immersed in oil. Needless to say, insulation is a must in a compact 
design like this and all leads are well and truly sleeved. The 
secondary leads are going to be brought out through hollowed out 
perspex pillars and use heavy neon sign type insulated wire.
     I decided to build this thing because I was fascinated by the 
drawings of the discharges in the AIEE lecture notes. It was clear 
that at this stage of experimentation, Tesla didn't know the rules 
applying to tuning and obtained all sorts of effects by attaching 
capacitances of various sizes to the hot ends of the secondaries.

M