[Penthode]

Been busy on CT100 this past week. Successfully installed my circuit permanently in the CT100. Convergence is very good if not better than the original transformer.

(Was delayed unfortunately by not one but three totally unrelated issues that required a bit of sleuthing! All part of the fun and more about that and related issues later.)

For the construction and installation of my solid state replacement unit, I shaped three perforated boards to fit in the transformer can. They are stacked and held in place with stanchions that would neatly fill the box. The picture describes my construction.

The tapped secondary of the original transformer connects to three points: to the convergence electrode, the focus electrode and the focus control 3000v source. I replaced the tapped secondary with a resistive divider. The focus control may be considered as signal zero or return so the capacitive coupled output of my circuit connects to the opposite side of what was originally the transformer secondary with a divided down parabola output to modulate the focus. For increased reliability, I saw no need to bring these three leads carrying 3000v into the box and so mounted the resistive divider consisting of 2w 560kohm and 330kohm resistors across the three points previously connected to the secondary.

The leads from the box are yellow the capacitively coupled parabola output, red to +400v, blue to the 12AU7 vertical convergence amplifier, black to ground and white to the diode junction of the main rectifier doubler. The white wire is to feed the internal doubler circuit to effectively create a voltage quadrupler to provide the +850vdc for the mosfet parabola amplifier. The white wire I discretely ran with the set wiring along the rear chassis underside and up to and after the main 400 volt rectifier fuse.

After installing I was concerned about the heat dissipation of the load resistor and the resistive bleeder to discharge the 10ufd capacitors. The resistors get only slightly warm but after an hour the box was reaching about 40 degrees Celsius. There was ample room to mount the resistors on the rear panel externally and had the added benefit to allow me to scope the 750vp-p parabola and measure the 850volt supply.

Below are some photos of the final install. The diagram I will add to the next post.