I don't think the mathematical approach works here, too many imperfections.
Anyway, i got ~130V out of the transformer and probably 50V to the cap. When i played around with duty cycle and frequencies i noticed a point where very few little bubbles seemed to come out of the tube, amp meter showed 0,1mA like always on the hv side, but i guess i must have been mistaken. couldn't find the point again later.
i wrapped the coil in saran wrap btw, 12V dc / <0,1A current.
next step is to find out how the bifilar behaves and then how it works together with the cap. i'll also change the frequency generator to 100Hz steps, i'll have a range from 0 - 100kHz then. the 1n4007 gets hot when there's a current >1A at the primary, will need to change it too.
the good thing is with the saran wrap the voltage on the secondary does not break down.