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Mulling over the failure of my circuit yesterday. Before the MOSFET died, Adjusting the Vertical Convergence Phase and Vertical Convergence Amplitude controls did react on the screen. Unfortunately I was unable to proceed further. I plan to purchase higher voltage MOSFET (800v) and look at presenting some gate protection.
Yesterday I managed to measure the peak to peak parabola at the plate of the 12AU7. It measured about 25 volt peak-to-peak with a simulated MOSFET input load. I emphasize simulated because before I had a chance to measure it, the MOSFET had already been destroyed.
Yesterday, I discovered that the 12AU7 plate waveform was inverted which will require an extra stage to invert the signal before presentingt it to the convergence/focus electrodes.
In addition, I do not see any noticable focus degradation not including the vertical parabola to the focus electrode. The vertical sweep angle of deflection is less. It is only the focus voltage which is applied the convergence transformer secondary since the vertical parabolais picked up capacitively by the Convergence electrode. However there is a degree of intreaction between Convergence and Focus Controls so it must have been designed that way for a reason.
I have attached my first stab at a two stage FET amplifier for the Convergence Transformer solid state replacement. I have also included screenshots from off-air signals this evening showing the misconvergence with out the Convergence transformer present. The greatest degree of misconvergence is the top of screen.
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