You are going to want to replace all of the capacitors in the power supply as you probabaly have low B+ and that would cause you to have low hv,how does your output tube look in operation????if the plate is red or glowing DO NOT run it for any length of time as you will destroy the tube,this means you have lack of sufficent h-drive whick could be due to a weak power supply,bad oscillator tube or a bad capacitor in the horiz section and yes this will cause you to have low high voltage.