Hi I've had better luck with 0 volts. If the tube has not been used for a long time, it will be a little gassy. This tends to boil

off the cathode along with the other stuff. When you have the voltage, the electrons will hit the gass atoms and ionize them. These are then slammed back into the cathode. One article I read stated that the first stage should be done with 0 volts and then switch to a + volts on the grid(s)+anode for the last part. I've not tried this myself but the method makes sense. In the first part, the getter has time to catch the outgassing. The last part helps to freshen the surface. I know that there are many articles that state to put the voltage on from the beginning. I've also read in a only a couple of articles that the outgassing from the initial stages can poison the cathode enough to make the process useless. I recover many old vacuum tubes for my old battery radios. I've had good enough experience with the 0 volts and enough bad experience with the voltage on the grid/plate that I use the 0 volt.