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

Quoting Kristian Ukkonen <kukkonen-at-snakemail.hut.fi>:
To: Richard Quick <richard.quick-at-slug-dot-org>
Subject: Re: GIF Files

 KU> I've made a subdirectory called pictures to the main tesla   
 KU> directory in the ftp-site and I have renamed the pictures    
 KU> like this: pica1024.gif becomes rq_a1024.gif - I presume     
 KU> that is ok? The documentations are included as a separate    
 KU> file like rq_a.doc..

Sure, this is not a problem. You might want to post again to the
group instructions for accessing the ftp-site where all of these
Tesla coiling files are stored. Do you still archive important
posts from the group to the site?

 KU> The pictures are great!


 KU> I'm interested in the modifications one should do to the     
 KU> coil shape in magnifying transmitters to get better          
 KU> efficiency as I'm most certain that after I finish my little 
 KU> 1/4 wave coil I'll switch to using them because they are     
 KU> apparently a lot more efficient compared to the input power  
 KU> vs. output.. If memory serves you mentioned in your video    
 KU> (and old postings) that the secondary coil can be a lot more
 KU> closely coupled to the primary and the proportion between    
 KU> height and diameter can be lowered.. I presume that you have 
 KU> a lot more experience about working set-ups now than you had 
 KU> at the time?  I'd be most interested in to hear more about   
 KU> this..

Yeah, the Tesla Magnifier allows the coiler to break thru the 50%
efficency barrier that is imposed on simple 1/4 wave coils. In
small Tesla coil systems this breakthrough is not a big deal; but
as power levels, and system sizes, increase, then the 50%
efficiency barrier becomes a brick wall. 

The problem with the 1/4 wave coil is that it is impossible to
force more than 50% of the tank circuit peak power into the
secondary coil. The secondary coil must resonate with this energy
to produce spark, but even with streamers issuing off of the
discharger, the pressure on the field flux linking the
primary/tank circuit to the secondary is enormous. Anytime the
spark gap goes unquenched for any length of time the secondary is
donating energy back to the tank circuit, and the efficiency
drops below 50%. This applies to even low powered 1/4 wave coils.

The more power fed into the 1/4 wave system, the harder the gap
is to quench. This quenching problem is not just because the
energy in the tank circuit is greater, it is also because the
secondary coil is electrically stressed more due to greater
excitation energy. The energy forced into the secondary coil is
not trapped there until the gap is quenched. When the secondary
coil is highly excited, the gap does not willingly quench at all.

Tesla saw this problem and devised the three coil Magnifier
system as the only reasonable solution. This development was
without precedent. In the Tesla Magnifier circuit a third, or
"extra" coil is added to the end of the system. At the same time
the secondary coil shifts it function in the new circuit.

The extra coil becomes responsible for 90% of the resonate rise,
or system VSWR. This "end resonator" is removed from the primary/
secondary field flux and is allowed to resonate unrestricted. The
energy supply to this coil comes in the form of RF current
supplied to the base wire by way of a transmission line
originating at the top of the secondary coil.

The secondary coil steps up voltage by a simple ratio of turns
transformation. Its pure resonance is highly restricted in its
new position, being responsible for only 10% or so of the system
VSWR. Since this coil is not functioning as the end resonator the 
design of this coil can be specialized to the new task: producing
the RF current used to base feed the extra coil. The secondary
coil can now be wound shorter and fatter with heavier wire. I
have found that an aspect ratio of about 1.5:1 on a coil form 14
inches or more in diameter works well. The secondary coil should
be wound with heavy wire, but since very high inductance is not
critcal here, a heavy stranded insulated wire may be used. Magnet
wire would likely work better, but based on the surplus prices of
PVC jacketed stranded wire I have not found magnet wire to be
cost effective. The secondary coil should be grounded to a heavy
dedicated RF ground typical of any Tesla system. It should be
noted that the system demand for a low impedance ground path and
ground are in excess of those normally encounted in 1/4 wave
Tesla coils.

The primary coil should be large and very closely coupled to the
squat secondary coil. Heavy wraps of polyethylene plastic may be
required between the primary and secondary to prevent arcing. I
have found that any and every means of insulation between coils
may well be required to obtain high efficiency in a compact unit.

The RF transmission line connection from the top of the secondary
coil to the base of the extra coil needs to be low loss. I have
used heavy gauge, fine strand, DC transmission cable (like
welding or battery cable) and lengths of copper tubing with

The extra coil needs a greater impedance than the secondary that
is feeding it. My experiments with low impedance extra coils have
resulted in no efficient systems, if I could get a spark at all.
The design of the extra coil can be made without the limitations
on aspect ratios, a shorter coil will frequently work better than
a longer coil designed for a 1/4 wave system. Even though the
impedance of the extra coil needs to be larger than that of the
secondary, too much impedance limits efficiency, yet the extra
coil is required to resonate at a much lower frequency than the
secondary coil for efficient systems. This is where it is really
helpful to have a variety of toriod discharge terminals available
for tuning and protection of the extra coil. 

The transmission line removes energy in the form of a high
voltage current from the top of the secondary to the base of
the extra coil some feet away. There is no longer any standing
1/4 wave in secondary, so electrical stress on this coil is
drastically reduced. By closely coupling the primary and
secondary, then using a fast quenching spark gap in the tank
circuit, it is possible for more than 50% of the peak tank
circuit energy to be processed through the secondary and into the
extra coil. 

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