Tube Coils, Toploads, and letting the Magic Smoke out

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Original poster: "sundog by way of Terry Fritz <twftesla-at-qwest-dot-net>" <sundog-at-timeship-dot-net>

 Hi All!!
 
Now, *before* the safety crew jumps on me, at all times this was under
control.  At least as much control as a TC of any type can be.  Some electrons
were hurt, but they have been treated and released this morning.   Now the fun
stuff!
 
  Mkay, I got to tinker with my tube coil last night, and it's just a trip.  
My power supply is an 1800v MOT with the doubler in place, the coil is running
in plain 'ole sputter mode.  Input power is 120v, 10-15A, depending on variac
position.  I keep it about 3/4 power most of the time, lower voltage on the
tubes and there is no real increase in output for the extra amp or so it
draws.  I'm running 2 833's, the plates don't even glow the tiniest bit. And
yes, I know this is pretty sad output for as much as this system should be
capable of, but I'm more interested in learning than getting 20" sparks for the
moment.  :)
 
  I tuned the coil with the secondary's topload, adding and removing topload to
get the best output.  
      My breakout is a neat folded-wire-stands-up-by-itself-thingey (technical
term) that can happily set in the middle of the topload and extends about 2"
above it to ease breakout.  With that in place, I get nice 5" sparks, of an
intense blue-purple.  Sweet :)   The real fun started when I added a 3" metal
sphere with a small sleeve and a nut on the bottom.  That part I pointed
upwards, and I removed the breakout.  About 1/2 variac power (usually already
making respectable sparks), I got no breakout, but every lflourescent in the
garage lit up *real* good :)  Surprisingly, there was no TV interference, and
only a dull hum in the radio in the house.  Anywho, at ~3/4 variac power, the
sparks literally exploded off the nut on the bottom of the sphere.  They were
around 6-7" easily, and instead of the blue-violet, they were the
whitish-orange at the base and middle, and the more familiar blue-violet at the
tips and the edges.  Much more powerful sounding and IMHO, more fun to look at
;)    
 
   But, it seems the RF kickback was *many* times worse without the breakout. 
I can see why, with all the reflected energy kicking around.  I use a 12A
breakered line conditioner (the breaker has been bypassed, it was weak and
tripped at 10A draw for any more than a second or so), but there is a 15A
breakout the conditioner plugs into, so it's breakered at 15A instead of the
30A the rest of the garage circuit is on, it keeps me from plunging the garage
into darkness.  Anywho!  The kickback must have been horrendous, because the
MOV's in my line conditioner kicked in with a loud *FOMPH!* and the Magic
Smoke, accompanied by some flames, belched outta the top of the unit. 
Whoopsie!  The 15A breaker popped, so I unplugged the filter, yanked out the
filament and MOT power, and chunked the smoking filter in the driveway.  There
it burned for a moment, then settled down and went out.  Lots of arcid smoke,
so I turned on my fan and went inside to have a coke as I pondered the
development.
 
It seems the topload of the tube coil adds a *lot* of energy to the streamers
once they can form, it's just the fine balance between them forming and not
forming that causes problems.  In the cycles the coil must ring up, all the
secondary energy is being shoved back at the tubes and plate tranny, but when
it finally does break out, it's got a lot more energy to push into the sparks,
hence the longer, fatter, more impressive sparks.  
   Does the breakout point on the tube coil tend to prevent the topload's
capacitance from adding to the spark length?
   
   In a spark gap coil, the tranny is effectively shorted when the gap fires,
so most of the ringing is kept out of it, but does the tube coil dump the
kickback into the plate tranny due to a lack of a sparkgap?
 
   Why did my total system power go down an amp or so when I removed the shunts
from the MOT?  Is the voltage doubler and low duty cycle of the tube coil
keeping the current draw down?  Shorted (while the shunts were in place), the
MOT would draw about 10A on it's own.  Without the shunts I haven't checked, as
it'll probably go chernobyl on me, and it's my last one.I still have most of
the shunts to put back in if need be. 
  
  Decreasing grid R will shorten the time the grid caps keep the necessary
voltage on the grid to keep the tube off.  Will decreasing grid cap C or grid
leak R increase current draw of the MOT?  How do I monitor current on the grid?
 
   
  On my "to do" list is finding a larger variac, building a proper control box,
and converting this coil to staccato.  
 
 Some particulars I find interesting...
     The Panasonic caps are working excellent, only a tiny bit of warming at
these power levels.  I'm using them for tank and grid C.  
     5w sand-filled resistors go *Boom!* when used for grid R.  A 5" length of
resistive spark plug wire makes a bit of a funny smell, but runs excellent
(4.8kohm!), is free (I got 2 old sets of wires), and is easy to work with.  It
didn't smoke even after a 5 min run at 8A input to the coil (I was playing with
flourescents and checking for TVI and RFI.)  
     I'm gettin irritable at all the RF burns I'm picking up working with this
thing. My tools, anything metal gives me a little BZZT!.  I found I can put a
screwdriver in each hand, get them ~10" from the topload, and get a nice steady
arc between them.  :)  Very cool! Tiny, but cool!  
    
       For probably the *first!* time, I ran a coil on and off for ~1/2 hour,
with *NO!* need for earplugs!  Ozone evacuation is still necessary though.  
                                                                               

  Comments, questions, etc are welcome! :)
                                                                           
                                                Shad