I'm taking a closer look at the Type 81 plug-in adapter I got with the 585A now that I have a manual for it. Basically, it is getting a full line voltage tap off the transformer primary, and it has it's own small transformer and bridge rectifier and power supply that is providing 75 Vdc for feeding series strung filaments (which many plugins use to tap other voltages off of by using the filaments as voltage dividers). Anyway, this is filtered by one of med's favorite cans...a 4 element 75 uF/150V apiece can. I suspect this is bad because every single one of the letter series plugins I have save for my Type Z exhibits horrible 60 Hz ripple that is all-pervasive. I suspect this is because the Type Z has it's own filtering going on, perhaps. Additionally, the Type 82 plug-in (which is made for the 585A and does not need the adapter) has zero problems.
Anyway, maybe tomorrow I will set it up and put a scope on that 75 volt rail and see if there's big ripple coming through, as I suspect there will be.