KM1H has good advice. I have gettered tubes by running in an old homebrew amp to get full filament voltage on the tubes. Then use your homebrew power supply as you outlined, but put a small voltage on the grid to control plate current. As you lower the negative voltage the current will rise, and the tube will begin to get red. Let it run like this for a few hours. That is why running it with full filament and the blower is important. If the tube starts showing a blue glow, you got a gassy valve. Whether there is any hope in that case is TBD. Carl probably could tell us. I had my hv ps (only, the rest of the rf deck was run on full voltage) on a small variac when I did this so was able to get the voltage up into the 1500 v range. Sometimes a tube would seem ok at 1000 v but when moved up higher (readjusting the bias pot/battery to control current) the blue gas would appear. Sometimes when I came back to check on it the 5 a fuse on the variac had blown.