Bert.. thanks for your comments,  you must know your tubes pretty well as all 
i gave was 16kv  max peak anode and you hit it right on the head 5c22. PIV on 
that tube is also 16kv..  during all new testing our coil is run from a 
powerstat which was only set at about 20% when the tube was anode firing and 
secondary was bad arcing out. So i dont think it was overvolted even 
considering nst/cap resonance.   trigger circuit is home built but creates a 
line synchronus, adjusted in time 350v trigger about 2usec wide.   
working now on using a cx1159 off of only one side of the NST.  Our 1159 
socket and filament circuit is originally designed for a ground thyratron 
cathode so we cant hang it accross both sides.