Preconditioning can double the life of the tubes, help restore a better vacuum by activating the getter, and will also reduce the possibility of premature arcing.Atmasphere, this is very interesting. All is not just 6as7g variant but ALL power tubes.
BTW this process applies to all output tubes, assuming they are new/untested or NOS.
If you apply B+ during that period the preconditioning process is ended.I assume this is not done during tube testing/matching?