I think there's an error in the schematic. Although I don't own one, I've used and worked on GLA-1000Bs and the tubes did not draw current in standby. The cathodes were floated way above ground in standby, using a high-value resistor (possibly 47K, I really don't remember) and that was switched to a bias zener on XMIT. It's very possible they made undocumented production changes, though. Almost everyone did! Henry was also guilty of that, although usually the changes made something better, not worse.