Bert, I am very grateful for your advice. The cap value was a typo in my mail. It is actually 0.01uF. I am also switching to a 6kv 15ma transformer and a 0.005uF cap some time soon. Also please remember that frequency was in KILOHETRTZ not MEGAHERTZ and is therefore a VERY long way from being a microwave. What are multiple spark gaps? are they in series, parrallel, how do you calculate the gap etc. Nick Field