Coil efficiency was Re: OLTC update - A problem!

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

Hi All,
   This is the set of guidelines that works best for me.  Your mileage may 
vary.

   A couple of years ago, I tested about 30 coils to destruction (except 2 
that didn't die).  I tried all kinds of aspect ratios, wire sizes, number 
of turns, toploads, cap sizes, breakrates, etc.  I put a whole lotta time 
into the setups.  I left the coupling the same for all the coils, to 
eliminate a variable that causes no end of grief.
   Here's the setup that consistently worked best for me.

   Using an aspect ratio of 4:1-5:1, between 1000 and 1200 turns (whichever 
gauge that works out to be).  For the toroid I use ~1.5x the secondary 
diameter, or larger as needed.  For the major toroid diameter, I use 
between 70-80% of the winding length (total toroid width).  Usually this 
requires a smaller toroid at the top of the coil to help with field control 
and corona suppression. For the tank circuit, I use as much tank cap as I 
can for the given transformer, running at 120bps.

    These guidelines usually give me a nice number of primary turns, which 
means high coupling with still plenty of HV clearance between the secondary 
and primary.  The goodly number of primary turns reduces surge current, 
which is good for the caps, and the massive topload and high number of 
turns gives me a pretty broad range to tune in (it tolerates out-of-tune 
situations better).  120bps is fast enough for the sparks to grow, but slow 
enough to allow for a considerable bang when the gap fires.  The LTR cap 
supplies rich, chunky amps of current across the primary, basically kicking 
the crap outta the base of the secondary to ring it up.  The huge topload 
does a good job of sucking the power out of the tank circuit, so quenching 
is quick and power-arcing rare.  It also provides a massive reserve of 
current for the streamer, so once it's formed it can stretch *way* out 
there, and if it connects to ground, the toroid current makes it pleasingly 
bright.
   With the LTR tank circuit, there isn't much kickback into the mains at 
all, and current draw is pretty smooth, if a bit high.  PFC takes care of 
that easily.

    The above combination has produced outstanding sparks on 2", 3", 4", 
and a 12" pig-powered coil (though we didn't get to test that 
fully).  Because I'm on a hiatus from disruptive coils for a bit, I won't 
be doing any work on them for a year or so, but I'm still chugging along on 
tube coils.  Possibly one weekend I can get back up north to Pensacola to 
visit James, and we can try that setup that we discussed.  Should rock like 
nobody's business.

  Hope it helps!
Shad
G5-1203