Transformer saturation trouble!
I have a VIC built and its working, it has 2.5km of 30 gauge wire on it, consisting of a primary of 32 ohms, secondary 180 ohms, L1 Bifilar 180 Ohms and L2 bifilar 180 ohms. Current problem is sorted but now I have core saturation even with air gaps above 9.5khz. It shuts down and refuses to oscillate above this frequency and current goes through the roof.
What core material should I use? Core is 10mm x 15mm to fit inside my coils btw.

Saturation caused from flux walking maybe?

Certainly with that many turns of wire and those low frequencies your core wouldn't saturate with a normal bipolar sign wave.  At least I wouldn't think so.

The only core material I can suggest at the moment is some kind of high frequency ferrite.  You can't saturate an air core, so start with no core and slowly insert the ferrite until the current starts to rise.  See how far you can get until you run into trouble.