How hot do a pair of Pass Labs X600 amps run ?

The 600 white papers say 150 watts. They act like there is more. The heat sinks are huge, and do get good and hot. Each amp weighs in at 150#.

As long as the heat sink temperature is not excessive, say above 120-130 deg F, it's normal for a pair of Class A amps to run warm enough to heat the room. When I run mine all day in the winter, the rest of the rooms in the house drop 10 degrees since the T-stat is in my listening room.

I have an X350 that I leave on continuously. It's roughly the same as one x600 monoblock. The top is slightly warm but the heat sinks are usually around the 'mug' temperature of a 3-5 minute old cup* of coffee.

I would say that it generates

A) Less heat than my ARC VT-100, old Aleph 2's, and likely
my BAT VK-5i tube preamp.

B) More than my old 185 W McCormack DNA-1, 200w Ayre V-1x,
and all 100-200w non-aleph amps I have used.

C) Around the same as my 4 KT88 tube AES 25 tube amp, and
possibly my 2 300B tube Cary 300-SEI

* The cup is glass, 3mm thick, green. My employer's stunning interpretation of an inspirational and appropriate substitute for employee pay increases. Rather pretty.

** Actually one of a set. The other being utilized as a spit cup in the upstairs bathroom.

*** Now that I think about it, I am strongly considering migrating the first away from coffee duty, and into a new role as a receptacle holder for decimated shellfish casings. Opinions ?

Think about a block of metal that's 19x12x22 inches that is hot to the touch but not so hot that you couldn't keep your hand on it. This is in your room radiating heat. For a typical listening room, this isn't terrible. Then there would be two for stereo. Another way to think about it would be to imagine a lightbulb array of comparable wattage -- the great majority of a light bulb's wattage is radiated in heat, not illumination. 600 watts of heat from an X600 would be like six 100 watt light bulbs. (Or one 150 watt light bulb, per the wattage cited in the above posts.) Notably, the heat radiated might actually decline very slightly as you turn up the volume, so long as you stay in class A mode, since more of the power draw would be consumed in making sound. Of course, it might get a teensy bit hotter when you start peaking into class AB. The X600 is a fine amp. Good luck.

to heat.

Conservation of energy. The energy is always there, though the form may change.

Draw 600 watts of electricity in an amp and 100% will be converted to heat. Even if some is used to produce sound, this sound will degenerate into heat as it is absorbed or otherwise dissipated.