Tube amps are inefficient. The maximum theoretical efficiency of class AB is 78% or so. The Dynaco MKIII is rated to draw 180 watts of power from the wall and it puts out only 60 watts of power. That would make it around 30% efficient. Horrible isn't it?
Not really, here is why.
How are we doing the environment a service if our new "energy efficient" appliances have obsolescent construction built in? The carbon footprint for mass producing non-serviceable consumer electronics must be huge. Also the chemicals, raw materials, and energy needed to make all that stuff must be astronomical as well. Its all made in China, where the environment has literally been ripped to shreds due to regulations that are non-existent.
It is therefore more environmentally friendly to run your old Dynaco's and service them when they fail, rather than replace your modern class D systems every three years after they fail. Doesn't it use less resources to replace a $0.14 resistor rather than the whole thing? I think so. I haven't done the math but common sense tells me that operating a MKIII for a few hours each day would cause less carbon emissions, etc rather than buying throw-away junk from China.
When polluting fossil-fueled power plants are decommissioned in the near and distant future due to fuel costs, the carbon and pollutions will largely become a moot point.
What do you think of the reverse environmental friendly argument for running tube equipment? You can apply the same logic to CFL bulbs with Mercury vs. regular incandescent lamps in a similar fashion.