Desire to underscan Horizontal
 

I have a need to greatly underscan a tube type monitor chassis. The reason for it is because I have replaced the 110 degree 8" 8HP4 rectangular tube with a 10" 55 degree round tube, a 10SP4. I have not changed the yoke yet. Maybe it will be done but it is worth it to try without it.

I've tried going to a lower tap on the H out. transformer but it's not working out too well. I noticed in another thread about a color set where it was suggested that an unwanted or excessive overscan could be reduced by changing a tap on the yoke. The function of this change merely put a 560pF capacitor in series with the windings.

On my chassis, a Conrac CNB-8, there is a width adjustment but I am at the end. I have tried putting a small inductance in series with the H winding and then to correct back down the overall inductance necessary for the circuit tuning, placed an inductor across the H yoke winding.

I have not tried a capacitance in series yet. Has anyone had experience adjusting tube set widths to unusually narrow settings or with using a tube having a lesser deflection requirement?

Mathematically, it looks like you want two more inductors:
Added inductor 1: same inductance as yoke, wire in series with the yoke winding;
Added Inductor 2: twice inductance of yoke, wire in parallel with the yoke/inductor 1 combination.

The net inductance will be the same as the old yoke, but the current in the yoke will be 1/2 of the old value.

Thanks. I had gone down that road but my inductors may have been saturating causing the poor linearity issues shown. This confirms I should revisit it with better quality inductors. They are not the easiest things to find.

I was able to buy some other yokes, 70 degree ones. The one in that set is a 110 deg.

I am sure the results will be better with the 70 degree yoke. The tube is a 50 or 55 degree tube, but that sort of yoke is older and not as easy to come by. neck size 1-7/8". still looking for focus coil(s), same diameter in "wanted' section.

Look at C613/C613A. If the "47k" values mean 47,000 pF (therefore .047 uF each, and about .1 uf total), you could also try reducing the value, or even disconnecting one of them temporarily.

They are 0.047uF each as you said. It won't harm anything to try it.