Magnifiers work very similar to normal classic TC's. They
basically behave as a normal TC with the secondary split into two
sections. The primary tunes to the combined secondary and extra
coil frequencies. In other words, the primary freq will be lower than
the extra coil freq, due to the presence of the secondary coil.
Although the coupling between pri and sec is tight, the overall effective
coupling is very similar to a normal TC. This all has to do with the
magnifier's behaviour as a system of coupled oscillators. The formulas
for figuring the tuning and coupling have been posted by Antonio Carlos
M. DeQueiroz on this list in the past. The higher the inductance of the
extra coil relative to the secondary, the looser the effective coupling
will be. I have verified the system's behaviour in actual working coils.
Since the coupling is actually similar to a normal TC, a normal rotary
or static gap will work fine. Quenching in a rotary has a lot more to
do with spark loading than with mechanical dwell time anyway. The
only problem with really long dwell times, is the gap can re-fire while
the gaps are still aligned.
Whatever break rate is best for a normal TC will be best for a magnifier.
There is nothing about a magnifier that calls for higher break rates.
I have never seen any proven efficiency benefit in magnifiers vs. normal
TC's. They do offer certain practical benefits, for instance the driver can
be left inside a garage or Tesla lab, and the extra coil alone can be
rolled outdoors for the production of long sparks. This may make the
set up a little more convenient.
I've researched magnifiers over the last 6 years or so, and built small
and medium sized coils up to 5kW, and also vacuum tube magnifiers.
I've documented my magnifier work on videotape, and I offer a special
VHS tape devoted only to magnifiers. To order, send $17 check or MO
49 Thiem Ave.
Rochelle Pk, NJ 07662
Contact me directly for overseas orders. Available in VHS NTSC format