I'm getting to that point, too.
This amp already had a standby in it (a 5E8 which is nearly finished), and in an other amp I had seen the "bright blue flashes," shortly followed by rectifier failure, that he describes on pg 47, and this looked like the quickest solution. I had always wired my standbys to switch the HV secondary, before the rectifier, so that the switch would not be switching DC.
I think I'll drop the standby completely in the future, at least for valve rectifiers.
steven