kazper said:
Does the higher voltages for the HV+ matter? I'm trying to understand what it does and why the 30-40V difference would matter.
It matters - because we're already stretching the ECC88's voltage capability to the edge (it's anode voltage is rated some 90-120V depending on what datasheet you consult)
Ca. half of our HT voltage appears across each half of the ECC88 - so the suggested 250V HT shouldn't be exceeded by too much.
On very-high-overvoltage units, there is a tendency of premature burn out of the tube.
Adjust voltage by trying different value resistors between resevoir caps - circuit sounds good between 200 and 250V.
Jakob E.