That might be a Class A amplifier.  In Class A, the amplifier is running its power supply at full power at all times, and drawing off the required power for the audio signal and wasting the rest to heat.  The reason for doing this is that the audio signal is then not dependent on the power supply being ramped up in time for a high power audio output.  If the power supply can not supply the required power in time for a peak audio signal, the sound quality is distorted.  And peaks can come very rapidly, such as with the start of a note on a plucked string (guitar, harpsichord, harp) or a piano string.  So Class A is basically considered the "best" sort of audio amplifier as it will never fail to ramp up the power in time.  I have an ancient Plinius SA 50 Class A amplifier (50 watts RMS output), and I have never found any need to upgrade it as it provides superb music.  I love Baroque music where there is a lot of harpsichord, and I originally got the SA 50 specifically for harpsichord recordings, although it also makes a lot of other recordings sound better too.  The SA 50 does need to be warmed up, but only for a couple of minutes - hours of warm up sounds as though there are other problems.  With a Class A amplifier, you generally only need a lower maximum power rating - with other classes of amplifier where the power needs to be ramped up, higher power ratings are often used so as to have more power available faster, rather than the maximum level really being needed.