First light of my directly coupled system

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz <twftesla-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>

Hi all:

After some time making only low-power tests and theoretical musings
with Tesla coils, I started to set up a full system.
My coil uses a direct coupling instead of a transformer, as shown
in the drawing below (use a fixed-width font to see):

                     (=====) Terminal
                        |
                        L2
           Gap          |
 o------+--o o--+-------+
        |       |
NST     C1      L1
        |       |
 o------+-------+-------o Ground 

I didn't tune the system yet, but made a quick test at full power.
It works, producing small streamers around the terminal and -hot-
violet arcs with ~8 cm to a grounded object. 
I dimensioned it for relatively low output power in this version,
and so the results are within the expected.
Not safe to touch. I tried to draw sparks to the tip of a screwdriver, 
and got a large arc that jumped over the handle and made two black 
spots in my fingers... 
C1 is an 1 nF MMC capacitor made with 10 10 nF 1000 V capacitors
(Siemens) shunted by 2 10 MOhms resistors each. Quite small because 
I want to try to power the system from a static machine too.
L1 is a quite large inductor made with #14 insulated wire over a 
10 cm PVC tube, that should have 315 uH of inductance (appears to 
have a bit more, detuning the system).
L2 is a long coil with 28 mH of inductance, made with 1152 turns
of #32 wire around an 8.8 cm PVC tube. Supported over a plastic box,
since the bottom is "alive" too.
The terminal plus the secondary coil should have a capacitance of
11 pF. The coil alone has 5.6 pF. I used a disk of thick aluminum 
foil in the tests.
The gap was made with 6 brass tubes screwed to an acrylic plate
through their centers, so I can adjust the 5 gaps in series 
precisely by turning the tubes around their centers:

     //////
o---oooooo---o
   //////

It needs some cooling. It would surely melt the base if operated
for more than a few seconds. Makes a lot of noise, and the brass
tubes turn to pink where the sparks form.
The ground connection in the tests was just a wire connected to
a metal bucket.
My NST produces a single, floating, 5 kV, 30 mA, output, and so
can be operated with one side grounded. I didn't
use filters or safety gaps, since the power is relatively small.
I preferred to connect the NST across the capacitor, but it's
also possible to exchange C1 and the gap. L1 prevents 60 Hz
voltages at the output, in any case.

The system was designed using my "multiple resonance" theory. It
operates in the optimal mode 9-10, oscillating at 270 kHz and 300 kHz
during the energy transfer, that takes 5 cycles of 283 kHz. 
The maximum voltage gain is 9.53. I didn't try to measure enything
yet, but the results are as expected, with ~5000 V of input leading 
to possibly ~50 kV of output.

By the next week I expect to have the system well tuned and
operating at maximum performance. I still have to make a decent
terminal for it. I will set up a page with pictures in my site 
after this.

Antonio Carlos M. de Queiroz