With linear amplifiers (classes A, A/B and B) you have a given rail voltage (usually 2 rails, + and -) and your output transistors modulate their impedance in such a way that the transistors create a voltage divider with your speakers. Your output transistors sink all the voltage that isn't going to your speakers. However they are not constant power because when the speakers receive less power, the transistors receive more voltage, but your total impedance is higher (because the way the transistors sink more voltage is to increase their impedance). This is why I personally advocate, when using linear amplifiers, to use those appropriately sized for speakers and room that you'll use them in. Because a higher power amp will have a higher rail voltage and if you're not actually using that power, then it's going to dissipate inside the amp and heat it up. The heat created in the amp is not itself linear however. You can lessen this effect and increase overall efficiency by using other class amplifiers like D, G or H. Class D utilizes PWM so the transistors basically create a specialized type of square wave that when run through a tuned filter it will result in an analog output signal. Classes G and H use multiple rail voltages and switch between them as your output power requirements vary. Those types of amps will still create heat, but can create less heat than the typical Class A/B amp.
In any case, more heat always means lower reliability in electronics, be it your computer or your amplifier. With computers it gets even more complex than amps (look up "electromigration"). But it still matters for amps.
Some receivers offer "eco mode" which you should use if you aren't using a lot of power. I had a Marantz SR7011 that was running hot when I was literally not using its built-in amps at all. Bad design there. Eco mode helped somewhat. I sold that receiver though. There was no acceptable reason for it to run hot when I didn't even use its amps. Onkyo runs hot too. You go to the store you probably see a bunch of cheap Onkyo junk on the shelf. Avoid that in my opinion.
Last edited by DonoMan; 06-26-2019 at 01:45 PM.