Large Coil's Output

 * Original msg to: Jwatson-at-students.uwf.edu

Quoting Jim Watson <jwatson-at-students.uwf.edu>:

> Thanks for your comments regarding my blown neon transformers.  

No problem. I was sorry to hear about the expensive trouble.

> I fired the large coil one more time with a friend at the 
> variac so that I could be very close to the secondary.  I 
> wanted to be able to tell precisely where the arcs were 
> originating, and where they were striking.  The arcs were  
> originating at the very top of the secondary and were 
> terminating at the very bottom of the secondary. 

I am currently operating a very similar system to yours I
believe, at least so far as the primary/secondary/capacitor
is concerned. I am not having any of the problems you describe.
What color is your primary coil form? While this may seem rather
off topic, I have seen plastics colored with carbon, which can
mess things up. I hope your coil form plastic is not black.

On the advice side: place a grounded strike rail above the
outside turn of the primary. This will reduce the incidents of
secondary strikes to the primary/tank circuit. This striking can
cause transformer/capacitor failure, but even worse perhaps is
that it can lead to arc shorting of the primary and a "runaway"
oscillator. The strike rail should be nearly a complete turn, but
should not be allowed to loop back on itself for obvious reasons.
The rail should be grounded to the system RF ground. I use
similar shielding over the spark gaps and tank circuit wiring/
capacitor if these things are likely to be struck with secondary
discharge. I find aluminum flashing to work great for this
purpose, but stand-off wires, metal mesh hardware cloth, or
chicken wire are all good tank circuit strike shields.

Next you need to play with your coupling. Using plastic, ceramic,
or even wood block insulators raise and lower the secondary coil
in relation to the primary. Does this have any effect on the
arcing up and down the secondary coil? Using the "CP" cap
purchased through the group I have found the coupling tends to be
rather tighter than expected. My 8.5 inch diam. secondary should
find my large flat primary (designed for a 10.25" secondary coil)
rather roomy and loose. Indeed this is not the case. The coupling
had to be loosened twice on my coil before all signs of splitting
(arcing and breakout) on the secondary coil were eliminated. This
was despite the fact that my peak-power/input-voltage were
deliberately kept low for initial power-ups, tuning, and break-
in. I try to light new systems up with 9000 volts or so before I
jump up to higher operating voltages. This is a good rule when
using either brand new or very old components.

Next you need to try adjusting your toroid height in relation to
the secondary. My current system is using an orange Tupperware
bowl for a standoff insulator. If the toroid is placed too high
it may not be doing it's job providing electrostatic shielding
about the the top of the winding. 

Richard Quick

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