[Penthode]

I have been running the CT100 the last couple of days with the my circuit transformer replacement. The signal amplitude appears more than ample to achieve full convergence.

The snapshots shows the progress made. Without the transformer removed and Verticak Convergence circuitry bypassed, convergence at the bottom and top of the screen could not be achieved. The first snapshot from 2024 showing the results of my first iteration, depicts bottom convergence made but top still out of convergence. I attributed this to insufficient waveform amplitude as I relied only upon the 400v dc supply. The last photo shows the top and bottom convergence made using the 850v supply. I think I can get the convergence better with a bit more tweaking and after I repair the intermittent 5Mohm Vertical Convergence Amplitude pot.

I have tried the circuit with a small variety of IGBTs and MOSFETs with tranconductances from 2mhos to 10 mhos and the results are similar.

I made minor variations to improve performance and reliability. The surge voltage on the 10uF 450v caps was about 490v, with is typically the limit for short term voltage peaks. I opted to but 500v electrolytics which I will use in the final circuit. I raised the 3.9 Megohm bias resistor to 4.7 Mohm to move the quiescent point up to prevent the MOSFET from saturating at full parabola amplitude. And lastly I included a pair of back to back 20v zener diodes to protect against gate source over voltage. This is an option and I thought about adding the zeners after I blew up an IBJT and MOSFET due accidentally miswiring the 47k gate to ground resistor and then powering up. (I made the same mistake twice!) I don't see this as a problem because ince correctly wired the gate should be pretty well protected.