another convergence question

[ohohyodafarted]

I will have more to offer on this subject in about a week. I am in the final stages of completing the restoration of the Hallicrafters CTC4 clone.. On my first attempt to get it up and running, the convergence was so far off I couldn't do anything with it. I discovered that almost all the pots on the convergence board were way off on value. After about a month of scouring the country for parts, I have completely rebuilt the convergence board with all new pots.

I would suspect that if you cant get good dynamic convergence on a ctc4 you may want to check the values of EVERY pot on the convergence panel. Especially the dual concentric 100 ohm pots that stick out the side. These 100 ohm pots are all carbon comp and it is my impression that they were not very durable. I have now built a personal stock of 100 ohm dual concentric pots that are all wire wound. I have no idea why RCA used carbon comp in this application. Wire wound would have been a much better option.

IN the past I have found the following to be helpful in addition to what has already been said about convergence. First of all if you are doing a convergence on a newly replaced crt, make sure you have the convergence yoke in the correct position followed by the purity ring and the blue lateral magnet.

The next step is to make your purity adjustments to get good pure scren colors. If you have the static red, blue and green magnets on the convergence yoke way out purity will not be correctly achieved. So what I do is put a patern generator using cross hatch and make sure the three color images are super imposed in the center of the screen first. Then I pull all the magnets on the purity ring at the front of the crt all the way out. At that point I disable the blue and green guns and go for the best red purity I can achieve following the purity directions in the Sams instructions. AFter red purity is good, I check blue and green for any impurity and touch things up using the pruity magnets at the front of the crt.

AFter purity is as good as I can get it, I set the cross hatch patern so that the center of the screen is misconverged by about 1/16 inch by turning the static magnets on the convergence yoke so I can see each color line individually. At this point I start to use the dynamic convergence board controlls to attempt to make the lines all parallel and equidistant from each other. When I have the lines as good as I can get them, I go back to the convergence yoke and reconverge the center of the screen using the static convergence magnets and the blue lateral.

And as was said before, convergence is a repetative process that gets better on each successive pass.