The 34401A arrived today, in barely adequate packing (1 layer medium bubble wrap, 1 layer screwed up newspaper, cardboard box, packing tape), nevertheless it seems in good order.
It has focused my attention on the fact that I really should move forward with my v-ref project; the HP and Siglent psus are good, but not 6.5 digit meter good, something I'd noticed but tolerated with the Keithleys so far.
The 34401, 2000, 2015, and 8840 all agree there is noise in the microvolt range on the outputs of these psus. Even the Agilent 1401B has a few uV of noise... I suppose I could go beyond the current twisted leads to coax to see if that helps, but I suspect not. But just for thoroughness, can anyone recommend a decent source of male 4mm banana to bnc or sma adapters?