* Original msg to: Kukkonen-at-snakemail.hut.fi

  <Talking about secondary in magnifying transmitter>

 RQ> I have found that an aspect ratio of about 1.5:1 on a coil   
 RQ> form 14 inches or more in diameter works well. The secondary 
 RQ> coil should be wound with heavy wire, but since very high    
 RQ> inductance is not critcal here, a heavy stranded insulated   
 RQ> wire may be used. 

Quoting Kristian Ukkonen <kukkonen-at-snakemail.hut.fi>

 KU> How heavy wire do you mean - something like #10 (2.588mm) or 
 KU> less ?

I would say that #10 AWG stranded is probably a little two heavy
for a starter Tesla Magnifier secondary. If you used #10 stranded
wire, and you increased the coil form diameter, it would offer
superior performance. The problem is that the physical size of
the system gets cumbersome and requires a lot of floor space, and
it requires a longer, heavier, and more expensive primary
conductor. For a starter project in Tesla Magnifiers I would look
at a #12 AWG stranded. Magnifier design is still in it's infancy,
and there are going to changes, omissions, and new input as our
experience grows. Best to cut back on the expense of starting out
by avoiding construction of a monster sized coil set.

 KU> I presume that you have actually done this with a setting as 
 KU> described above? What was it like - wire gauge, diameter     
 KU> etc?

I have wound and fired several secondaries in Tesla Magnifiers
that have worked well (and a couple that did not). In addition to
this I have pressed a couple of large and heavy coils that were
originally wound for 1/4 wave work into service as Tesla
Magnifier secondaries, with presentable results. In addition to
my hands on experience, I also have several excellent videos on
the subject that were produced by Richard Hull of T.C.B.O.R.. 
In my humble opinion Richard Hull is the leading expert on Tesla
Magnifier design and operation. Mr. Hull has devoted a tremendous
amount of resources to Magnifier development. 

Both Richard Hull and I have built systems that did not work at
all, or did not work as well as we had hoped. However, we have
both built some decent systems too (well mine are decent, Mr.
Hull has some EXCELLENT systems). I find that what works for
Richard Hull also works for me. 

I have a real solid Magnifier secondary that is 14 inches in
diameter with a winding length of 20 inches. This coil is wound
with surplus insulated stranded wire that happens to wind on at 
10 turns per inch. I do not know the precise gauge of wire that I
used, but my experience tells me that this unmarked spool of
surplus wire has insulation that appears thinner than standard. 
This coil resonates around 450 kHz.

 KU> Is the set-up above only good for power-levels of several    
 KU> kWatts and above or is it good for something like 1kW as     
 KU> well - or should it be smaller for this?

If you have a large enough primary coil, you should be able to
tune at power levels of 1 kVA. Power levels are increased by
adding larger and larger toriods to the extra coil and then
adding primary turns, and finally capacitance, to the tank
 RQ> The primary coil should be large and very closely coupled to 
 RQ> the squat secondary coil. Heavy wraps of polyethylene        
 RQ> plastic may be required between the primary and secondary to 
 RQ> prevent arcing. I have found that any and every means of     
 RQ> insulation between coils may well be required to obtain high 
 RQ> efficiency in a compact unit.

 KU> What exactly did you use for the primary - heavy copper tube 
 KU> as a helical coil? What was the set-up like - proportion     
 KU> between sec. and pri. diameters, heights etc..

Yup, a heavy soft copper helical coil. About 15 turns, about four
inches larger in diameter than the secondary. Coupling can be
adjusted by raising and lowering the secondary coil inside of the
primary, but figure the primary will come about 1/3 of the way up
the secondary coil.  

 KU> In Scientific Instruments Reviews a "few" years ago there    
 KU> was a description of a Tesla-coil (in inert-gas tank etc.)   
 KU> that used only one turn in the primary - a large piece of    
 KU> copper plate to be exact.. I guess that it was not too       
 KU> efficient.. 

I honestly believe coils such as this were designed using
mathmatical tools derived from radio theory. The single turn
primary has a good following among "radio theory" coil designers.
This allows for the maximum possible ratio of turns transform-
ation between the primary and secondary. But this school of
design appears to ignore the fact that most of the voltage rise
in a Tesla coil is due to resonate rise, not just simple trans-
formation. Efficient resonate rise requires efficient intro-
duction of energy into resonator, something a single turn primary
fails at miserably. In addition to the above mentioned problems,
a single turn primary puts a brutal strain on the rest of the
coil system, especially the HUGE tank circuit capacitor required.

 <Talking about extra coils> 
 RQ> the impedance of the extra coil needs to be larger than that 
 RQ> of the secondary, too much impedance limits efficiency, yet  
 RQ> the extra coil is required to resonate at a much lower       
 RQ> frequency than the secondary coil for efficient systems. 

 KU> Your ancient :) text describes that the primary and tertiary 
 KU> coil are of the same frequency and the secondary is twice of 
 KU> the frequency before - I guess this is the basics? 

Yes, it is the basics, though it is really more complicated. The
tank circuit and the extra coil are tuned to the same frequency.
The secondary coil is then forced to produce a fractional wave
signal that is heavy in current. The most efficent fractional
wave signal produced by the secondary would be the 1/8th wave
node, which offers both current and voltage. By tinkering with
the resonate frequency of the extra coil by adding and subtract-
ing toriod, it is possible to force a 1/8th node on the top of
the secondary and along the transmission line. However, I have
seen systems operate on 1/16 wave output from the secondary, and
there are a number of other modes of output that will work. 
 KU> As one uses a very high break rate on the rotating spark-gap 
 KU> - will one have to put in a _lot_ of power to be able to     
 KU> fire the cap as ofter as it should or will one use a very    
 KU> small cap or ?

Magnifiers are amazing for the conservation of capacitance. Tank
circuit configurations can be used that are responsive at lower
break rates, but I have long been an advocate of the balanced
Tesla tank circuit for high performance, and after about two
years Richard Hull was finally convinced. I saw the video of his
Magnifier right after he switched over to the balanced circuit,
when he was able to really rev the gaps and pour on the juice...
The spark got longer and longer, and no other changes in the
system were required. The reason behind this is that the
capacitors are made to pulse more often, not with more power.

 KU> I have some huge fiber-glass tubes (nearly a meter in        
 KU> diameter) that might be of use - they have walls about 10mm  
 KU> thick though.. :( but the height to diameter proportions are 
 KU> about exactly correct.. :) 

I would go with something like a polypropylene flower planter.

 KU> Thanks for the information! 

Hey, no problem.

 KU> I really intend to build a system like described above..

Great! And best of luck!

Richard Quick

... If all else fails... Throw another megavolt across it!
___ Blue Wave/QWK v2.12