Why no heated gear?

I'm surprised that Elizabeth gave up. Or maybe not, judging by some of the other comments. So let's examine this issue from the ground up.

When we say that a piece of (tube) gear needs to "warm up", what are we specifically referring to? Does the audio quality change because the case is warm? No. The knobs, wiring, lamps and switches? No. The PCB, if present? No. The transformers? No, not so much. The tubes? Aha! Now we are getting somewhere.

So why does the sound change when a tube heats? To keep it simple and avoid big words like anode and cathode, let's just say that a physical change occurs between the tube's internal elements. A tube does not operate efficiently until all elements reach the optimal operating temperature. While heat is required for the tube to operate, too much heat will destroy the tube. In fact, one of the reasons that power tubes need to be biased is to compensate for the heat potential between the an... never mind.

So why can't we just heat the tube with an external heat source like a heat gun or a heated blanket? Because "tubes" are vacuum tubes - the glass envelope encases the internal elements in a vacuum. No gas (atmosphere), no heat transfer can occur from OUTSIDE the envelope. See what you can learn when you don't sleep through High School physics class?

Herman, thanks for helping me to win a bet with myself. When I wrote:

So why can't we just heat the tube with an external heat source like a heat gun or a heated blanket? Because "tubes" are vacuum tubes - the glass envelope encases the internal elements in a vacuum. No gas (atmosphere), no heat transfer can occur from OUTSIDE the envelope. See what you can learn when you don't sleep through High School physics class?

I just knew that you were going to reply the way that you did. OK, you caught me. I am guilty of a gross oversimplification.

The fact is that the glass heats up when a tube is powered because of radiant heat. But it's an inefficient process, and radiant heating from a high temperature source in close proximity is a very different process than "warming" from a low temperature source from several inches away. Do you possibly believe that you can pre-heat a tube to anywhere remotely close to operating temperature? Actually, that is done (sort of) for certain types of specialized lab gear and of course cold cathode tubes, which operate at a much lower temperature. But it wastes a lot of energy and can't be done except in controlled conditions.

And regarding your last statement that there is no such thing as heat potential in a tube. Really? So you believe that the anode and cathode in a typical vacuum tube are EXACTLY the same temperature? Planck's Constant indicates otherwise. So between your opinion and Max Planck, I'll take Max.