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Magnifiers revisited
---------- Forwarded message ----------
Date: Tue, 7 Oct 1997 10:01:28 -0400 (EDT)
From: FutureT-at-aol-dot-com
To: tesla-at-pupman-dot-com
Subject: Magnifiers revisited
All,
I've built a few magnifiers over the years, one of which gave an 80"
spark. Whenever I want to explore some aspect of a magnifier, I
toss one together and do some tests. Perhaps this data will help
those who are just entering the magnifier arena.
Today, I decided to convert my 42" spark classic TC into a magnifier
to observe the quenching and overall performance. This was
accomplished quite easily by using an old 6 1/2" by 6" tall secondary
for the driver secondary (#28 magnet wire), and using the original tall
secondary as the new magnifier extra coil. The remainder of the coil
remained exactly the same; .007uf cap, 8 point series quench rotary,
120 BPS synchronous, 5" by 20" toroid, etc.
At first the driver was loosely coupled at .29, the pri. tap was moved
out by 2 turns, and the coil was run. Sparks hit 40", and hit 44" one
time. Sparks also reached 44" on occasion in the classic TC. The
magnifier sparks however appeared to be less bolt-like, and appeared
more plasma-like. Instead of hitting the measuring wire with a snap,
they seemed to hit with a wispy sizzle. Overall, the coil was weaker,
and the average sparks were shorter.
Next I gradually increased the coupling to k = .39, but the sparks
weakened as the coupling was increased. The sparks appeared
sluggish and dull -- the classic signs of poor quenching. Just to
be sure that the 12kV, 30ma tranny was still ok, I loosened the
coupling back to k = .29, and the sparks increased in length. If I
tried to increase the coupling beyond k = .39, problems with arc-
over occured since this coil was not originally designed as a
magnifier and a saucer primary is being used.
Observing the quenching using a solid state scope, I saw that at
k = .29 the quench occured at the 2nd notch, and at k = .39 the
quench occured at the 3rd notch.
BTW, the driver secondary L = 20mH, and the extra coil L = 100mH.
The primary has 42 turns and is tapped at 35 turns as a magnifier
and at 33 turns as a classic TC. Input power was 740 watts in each
test.
Conclusions and speculations:
1) This series quenching rotary does not quench well enough for a
small magnifier (toroid sized for max spark length) at 120 BPS.
It is possible that a higher break-rate would create a
larger ionized load around the toroid and promote
better quenching but I did not try this. I suspect that any benefits
would be marginal at best. This series quenching rotary is barely
adequate for a small classic TC and quenches anywhere from 1st
to 3rd notch. Perhaps the rotary could be improved by using a
larger diameter rotor, adding air cooling, etc.
2) As I tightened the coupling, the quench degraded and the sparks
weakened. A magnifier probably requires multiple heavy streamers
to promote good quenching. If I had cranked up the power, the
quench may have improved and the spark may have lengthened,
but I would have obtained a decreased "efficiency" as measured by
power input vs. spark length.
3) The relatively low frequency used did not solve the quench
problem, however low frequency operation is theoretically a plus.
4) The greatest hurdle blocking the success of small magnifiers
is the attainment of adequate quenching. Anyone contemplating
the construction of a small magnifier should be prepared to deal
with the above issues. In general, quenching is assisted by spark
loading, so the larger the output sparks, and the greater the
number of steamers, the better the quenching will be -- the gap
can only do so much. In large magnifiers, the heavy spark loading
probably helps the quenching, but other types of problems move to
to forefront.
John Freau