Predicta 17" HV question

[DaveWM]

It also looks like it is borrowing some neg bias from the horz out grid circuit. I would check R58 and R59 which makes up a voltage divider for the bias and also scope the grid of the 6DR7 pin 2-3. sometimes the neg voltages at the pins can be misleading esp if that bias supply is goofed up due to a faulty divider network (R58/R59). oh and check C50 the .22 cap that looks like it filters that bias supply.