Poor results

Well, last night I finally set up my coil outside for its first run since I
built my new ground system and reconnected all my primary components with
3/8" copper tubing.

I placed a ground rod about 3 to 4 feet away and layed a piece of wire on the
toroid pointing toward the ground rod.  I fired the coil at low power.  The
welder was set at 55 amps.  I had 18 amps of primary current into the pole
pig and the pole pig primary voltage was at 175 volts.  I had nice hot arcs
to the ground rod.  I tried several different primary tap positions trying to
find the best tune.  Then it was time to go eat dinner.  I came back out
about 45 minutes later and refired the coil.  Now something was screwed up.
 The gaps were firing inconsistently and the sparks from the coil were weak
and purple.  The primary pig current dropped down to 12 amps and the primary
voltage was up to 240 volts.  I shut everything off and pulled the cover off
the rotary gap thinking something was wrong there.  I could not find any
problems with any components or wiring.

There was a weather front coming in and I noticed the humidity had gone way
up.  Things weren't wet but there was a noticable dampness in the air and on
the wood surfaces.  Is this the problem?  Does anyone have any ideas?

How about this method of tuning at low power - do other folks do it this way?
 Will the frequency change after I remove the wire from the toroid and turn
the power up?  Richard Quick and I have discussed this somewhat and concurr
that there does seem to be some lowering of frequency going from low to high
power probably due to the larger electron cloud around the toroid at higher
power effectively making it look bigger and lowering the frequency somewhat.
 We agreed there is a 1/4 to 1/2 turn difference in tune on the primary
because of this?  Has anyone else seen this?

Ed Sonderman