CT-100 B1001599 Failed Convergence Transformer

[Penthode]

I received my components delivery from Newark this week. Thye past two evenings thinking over the electronic transformer component with the MOSFETs.

I tried initially with the single power MOSFET inverting amplifier. The results show is that the single inverting amplifier does pull convergence in the correct direction and does offer improvement.

The problem I am running into is insufficient amplitude. Using the CT100 400 volt power supply and a 900volt max. drain to source mosfet, the maximum linear amplitude is 350v p-p. I need a bit more!

I had to reduce the 12AU7 plate resistor to 10k to curb it's output amplitude feeding the mosfet It looks as if the 12AU7 typically delivers up to 50v p-p to the original transformer. I cannot use any more than about 35v p-p before the mosfet clips.

My next thought is to use a small step up transformer. It could be an audio transformer and I would only need less an a 2:1 ratio. Further, why not try a standard audio transformer and capacitively couple to the high voltage convergence electrode? The transformer would then be spared the stress of the high voltage and a 10:1 ratio should be easily achieveable.