series resistors

Hi All,
	I was running my coil at the weekend and trying to hit the sweet spot on
the tuning. i was getting regular 24" sparks to a grounded small toriod. I
though I would try out a difference transformer (10kv) instead of the 9kv i
have been using. I changed the primary tap point be one turn . This
transformer did not seem to work. I will do a continuity test on it when i
remember where i put my meter. I then replaced the 9kv transformer and
changed the primary tap point back to roughly where it was before (about 11
1/2 turns) and run up the variac. The spark length was reduced to 15" and
the safety gap was firing hard. All activity stopped. When I checked I
noticed that one of the series resistors had got hot enough to melt the
solder and the resistor had become disconnected. I assume this has been
caused by rf kickback put am puzzled as to why. Any ideas?

bob golding