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Quoting Kristian Ukkonen:

 KU> I'm sorry for the series of errors I've made with my comments on your
 KU> magnifier secondary.. I don't know what I'd been thinking or doing -
 KU> I did type in the specs last night and got about the same result as
 KU> you said - and my coil will resonate at about 230kHz.. Anyway, it
 KU> was a mysterious error of mine..

Ahh, don't worry about it. My math skills are so weak that I would not,
could not, attempt even the simplest manual calculations without making
multiple compounding errors. I need a calculator and a computer for
any figuring. This is perhaps another reason I get annoyed when people 
start insinuating that math is the solution to the perfect Tesla coil 
design. I think math is the PROBLEM!  (At least for me anyway... :-)

 KU> I've got a really nice idea of the primary step-up xformer: I found
 KU> a place where I can get for free 4kVA cores.. So, I will make the 
 KU> windings (which will take some time to wind) and get a nice
 KU> xformers with the specs I like.. The core has places for four
 KU> coils so I will have to divide the primary and secondary into four
 KU> coils with sec over primary.. Anyway, I can easily get either
 KU> 5kV, 10kV, 15kV or 20kV out by taking a tap out from the leads between
 KU> different parts of the secondary.. I'll have to do some further 
 KU> calculations but the formulas I used recently to approximate the
 KU> coils did give result stating that less than 1 turn/volt could be
 KU> used which would implide than primary about 220 turns, secondary
 KU> 20000 turns.. This sounds a bit low an amount of turns so it must
 KU> be checked but otherwise the idea sounds wonderful. 

The book: ELECTRICITY AT HIGH PRESSURES AND FREQUENCIES 
Henry L. Transtrom, originally published: 1913, second edition
1921, Joseph G. Branch Publishing, Chicago; Reprinted 1990, ISBN
1-55918-054-4, Lindsay Publications, Bradley, Illinois, 60915.
Paperback, 247pp, Lindsay # 20544, $ 11.95.

Would be a helpful guide. They have explicit instructions for the
construction of a homemade transformer for Tesla coil use. These
instructions include all of the formulas, coil winding guide and 
techniques, pretty much everything. It also has a chapter on building
a current limiter for the completed transformer. Just a suggestion.

 KU> One of the remaining questions is whether to use oil-immersion 
 KU> or not - it might be dangerous as the xformer might fail etc. 
 KU> and the burning oil and possible explosion does not sound nice..

I don't know what it is with people and the fear of oil explosions
and fires. I have melted down wire in oil submersed HV components
and never got more than a "burp". I have blown oil submerged caps
clear through both plates and dielectrics, again nothing more than
a "burp". The oil takes a long time to get hot enough to become
dangerous. In properly design caps and xfmrs things simply do not
get that hot. Failures do occur, but there is no oxidizer in the oil,
so there is nothing to combine with to cause an explosion.

An explosion requires a poorly designed component or a component
that is not rated for Tesla applications. A good example here are
these sealed glass HVDC filter caps. They are submerged in oil.
These caps are sealed. They are DC rated. They get hot. They explode.

A homemade cap or transformer is hopefully over-designed enough to
compensate for the fact that they are home constructed. They should
be vented to normal air, and they should be properly circuit protected
(fuse or breaker) and safety gapped. You check them frequently to make 
sure they are not overheating until you learn the operation character-
istics. Under these circumstances there is less chance of fire under
oil where the oxygen is displaced, than in open air.

 KU> I did pick some nice chokes as well.. 7 and 9 mH, 16A.. These 
 KU> things are heavy! and should provide excellent filtering..

Great!

 KU> I'm slowly gathering the equipment for the magnifier as I think I
 KU> should increase filtering a lot those chokes were a great
 KU> discovery for practically free..

Magnifiers produce a lot more RF that needs to be filtered. They will
also give your bypass caps a workout.

 KU> Oh yes, I'll probably pick some magnetic valves for the air-blast
 KU> gap as well.. I can after that control the flow of air from the
 KU> control panel - I'll be using a tank of pressurized air through
 KU> a variable-pressure valve..

That is always nice, and saves on the air.

 KU> An interesting idea was uttered today: how about using a normal 
 KU> cascade to step-up mains voltage up to, say, 11kVDC and use this
 KU> to load the primary capasitor.. It will need extensive filtering
 KU> but this will be possible as the primary xformers is eliminated and
 KU> thus large capasitances can be present etc.. We'll have to test this
 KU> idea with Harri to see if it will work - it would be a major change
 KU> in costs as the diodes would be dirt-cheap as well as the caps neede
 KU> for cascade and filtering.. Of course, the filtering is the main
 KU> question as otherwise we would be blowing diodes and lots of them
 KU> in a single kick-back.. I'll tell you more about this later..

This has been done on normal Tesla coils, but I don't think anyone
has run a Magnifier on DC inputs. Magnifier kickback is another area
discussion entirely. 

 KU> About the CW-coil : we've got about 20cm of discharge and lots of
 KU> problems have (apparently) already been solved after blowing up 20+
 KU> FETs.. 

You just let me know when it is debugged and I will happily build one...

Richard Quick


... If all else fails... Throw another megavolt across it!
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