Like Wirehead I'm a fan of space-tech labs. the most simple answer to your questiong i've ever found is written by albert on space-tech's website which i'll post below. you can read more easy-to-understand comments about tube gear at space-tech-lab.com
Q1. Why tube sounds better ?
Ans :
There are several main reasons that makes tubes sounds better , the following list out those points,
1. Tube is a much more linear device than transistor during operation.
2. Due to the highly non-linearity , conventional transistor amplifier must have very heavy NFB (negative feedback ) to make it work stablely, but tube amplifier can work well with very little or even no NFB, and heavy negative feedback is well known today as one of the main reason of poor sound quality.
3. Tube is a totally mechanical device, inside a tube is just some metal plate arrangements, the effective operation area is much much larger than a semiconductor (sometimes even 1,000,000 times larger). Almost every gold-ear audio engineer should knows , when music signal pass through a very small area, it will implies certain squeeze feeling to the signal itself and it is very audiable , so when a signal just pass through one transistor, you will immediate sense the compressed , flattened and hardened feeling from the music. The more transistors , it kills the easiness more and give your more flatness and hardness to the music.
4. Tube-amp has higher THD (total harmonic distortion) than transistor-amp by testing, but those THD created by tube-amp is all even harmonics which is very pleasant to ear and will not feel disturbing unless it is > 12% . But transistor-amp gives out odd harmonic distortions which is highly un-pleasant to human ear, by actual experiment, just 0.2% of odd harmonic distortion is audible and will create un-pleasant feelings even to un-trained ear.
Q1. Why tube sounds better ?
Ans :
There are several main reasons that makes tubes sounds better , the following list out those points,
1. Tube is a much more linear device than transistor during operation.
2. Due to the highly non-linearity , conventional transistor amplifier must have very heavy NFB (negative feedback ) to make it work stablely, but tube amplifier can work well with very little or even no NFB, and heavy negative feedback is well known today as one of the main reason of poor sound quality.
3. Tube is a totally mechanical device, inside a tube is just some metal plate arrangements, the effective operation area is much much larger than a semiconductor (sometimes even 1,000,000 times larger). Almost every gold-ear audio engineer should knows , when music signal pass through a very small area, it will implies certain squeeze feeling to the signal itself and it is very audiable , so when a signal just pass through one transistor, you will immediate sense the compressed , flattened and hardened feeling from the music. The more transistors , it kills the easiness more and give your more flatness and hardness to the music.
4. Tube-amp has higher THD (total harmonic distortion) than transistor-amp by testing, but those THD created by tube-amp is all even harmonics which is very pleasant to ear and will not feel disturbing unless it is > 12% . But transistor-amp gives out odd harmonic distortions which is highly un-pleasant to human ear, by actual experiment, just 0.2% of odd harmonic distortion is audible and will create un-pleasant feelings even to un-trained ear.