You definitely have a problem in the flyback supply, including the horizontal output stage. You have already proven that the CRT is not loading it down. Voltage checks should reveal the cause. Have you checked the B+ BOOST voltage? Since you have two voltages that are low, each supplied by separate windings on the flyback through separate rectifiers, I think the problem is more likely to be in the horizontal output & damper circuits. Have you swapped those tubes?