I disagree with this, well I disagree that it is implicating that tube amps are inherently noisier than other types of amps. This is definitely not the case. Any amp can be noisy.
db/mw is a bad way to look at whether a particular thing will be noisy. There are quite a few high impedance headphones pushing close to 100db/mw after all... you have to have an especially speshul amp for someone to say that they are noisy. (A high gain SS amp with high impedance feedback/input impedance setting resistors should do just fine). db/mv is a better standard if you want to look at noise.
I will as is me perogative stick by what i said. Tube amps are noisier than SS amps,in fact as you know they excell at picking up mains hum which to me is totally unacceptable,and at the price some sell at nothing short of outrageous.
Yes there are good and bad with all but in this day and age NO amp should exhibit noise, more so if it sells itself as a "headphone amp".