Despite being nearly 100 years old, Tube technology still sounds great and are still popular with audiophiles and musicians.
Tubes, like analog recordings, have a more full-bodied sound than transistor components. There’s a “roundness” to tube sound that solid-state components never equal.
Tube amplifiers soften the peaks before the sound becomes audibly harsh, so it seems to play louder than it should. A tube amplifier is usually considered to sound more ‘graceful’ and more musical on acoustic music and voices. The best amplifiers will combine both characteristics.