Liquid Cooled!
Bob Reina stopped me in the halls and asked, "Have you heard the water-cooled triodes?" Huh? Turns out the $59,000/pair Von Gaylord Audio Uni Signature Editions monoblock power amplifiers use exterior transmission-grade tubes submerged in an oil coolant, I presume and you can really see the thermal motion of the coolant, so I'm guessing the tubes run <I>hot</I>.