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Connected up the breadboard circuit to the CT100 for a test today. The wider voltage swing was sufficient to bring in convergence. I can get a parabola amplitude of 750 volts p-p.
The using the voltage quadrupler extra two diodes and electrolytic capacitors to augment the ones in the set to boost the B+ to work my circuit worked very well. Too well in fact because on power up the voltage rises to 950vdc before it settles back to around 850vdc. I measured the peak voltage across the two 10uF electrolytics in may circuit and it rises to 485 volts on power up before settling back to about 425vdc each. I will have to study the surge rating of the capacitors. Might end up stacking two pair just to be safe.
I found I had too much gain. In the drawing I posted a few days ago I forgot to include the series 22k resistor to the gate. I raised the 22k to 56k. I also reduced the input coupling capacitor to 0.047uF.
I will run it for a few days in breadboad form before building the circuit to mount in the original transformer box.
I am happier with this approach as the components are cheap, it requires no modification to the set apart from running one additional wire to the set's voltage doubler, it only uses 2mA current and I don't have to deal with that fragile convergence transformer.
The picture of the crosshatch was at initial power up with only a preliminary touch of the controls. The subsequent off air photos were after further convergence touch ups.
I am finding the convergence perhaps better before the transformer failure which suggests it was destined to fail.
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