Step 1: Danger, Will Robinson, Danger!
This is dangerous, high voltage stuff. OK, it's not "High Voltage," technically, but it's high enough to kill you. The power supply in this projects kicks out 200V, which is plenty, with startup spikes near 240V or more...
Don't believe it when they say "it's not the voltage, it's the amperage that kills you"--because it's both. Amps AND volts together dictate the danger level. If it were amps alone, then even a AA battery can supply many times what's needed to stop a human heart. The volts do the "pushing," and overcome the natural resistance of your skin. And there's plenty of current available to harm you in any tube audio amp...
--Always drain the power supply filter caps before touching the circuitry.
--Always unplug the mains cord before working.
--Double-check (with a VOM) to be sure the filter caps are drained.
--DON'T mess with this stuff unless you have a decent understanding of the dangers.
--DON'T mess with this if you believe you know EVERYTHING about high voltage, and think that makes you immune to electrical shocks.