A8, B8, C2, and C5 are the heater supply and should be close to 6.3 volts DC. If your measurements are accurate (no dead batteries in the meter, etc) then the heater supply is at fault. I would suspect a bad solder joint on one or more of the Schottky diodes - if it's operating as a half-wave with a missing diode, that would drop the voltage.
A4 and A5 are the grid and plate respectively of the driver section. The fact that they are so close in voltage suggests the possibility that they are shorted together. A6 is the cathode, and the slightly low voltage indicates a bit less than the C4S current is flowing there, which would make sense if som of that current goes from the plate/grid through the 220 ohm grid stopper and volume control to ground. If you can't find anything and re-heating the solder joints does not help, swap the tubes to see if a tube has developed an internal short.
It's a start ... :^)
