The simplest way is to draw 5k line on Ua/Ia/Ug diagram, for example through 400V/0mA and 80mA/0V points on X and Y axis (400/0,08=5k). Then you can try various other 5k lines, parallel to the first (preserving the same angles) and various operating points on them. Then you can explore voltage and current "swings", power, linearity, etc.