Vacuum-tube amplifiers are not in the same class with techniques that are unlikely to have any perceptible influence on what you hear.
Among amplifiers that are not perfectly neutral, vacuum-tube amplifiers subjectively seem more pleasant.
Moreover, while an electronic audio amplifier made with modern components can be made perfectly neutral when terminated on a resistive load, i.e. it can reproduce any input signal without any changes except amplification at its output, once you connect loudspeakers at its output the amplifier-loudspeaker chain is no longer neutral, i.e. it no longer has a flat transfer function between the electrical input and the sound output and it is not at all clear which should be the output impedance of the amplifier as a function of frequency to ensure the least degradation of the sounds in comparison with the input signal.
So it may happen that a vacuum-tube amplifier - loudspeaker system has actually a better overall fidelity than a typical audio amplifier that was designed to demonstrate a much higher fidelity on a resistive load (because thus the transfer function is easy to measure and correct, unlike the complete transfer function to sounds).
In theory, one could make a modern amplifier reproduce any quirky behavior of vacuum tubes, e.g. a higher and frequency-variable impedance or certain kinds of distortions, but usually nobody bothers to do this, because it would be expensive and the normal amplifiers are good enough for the majority of people.
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Vacuum-tube amplifiers are not in the same class with techniques that are unlikely to have any perceptible influence on what you hear.
Among amplifiers that are not perfectly neutral, vacuum-tube amplifiers subjectively seem more pleasant.
Moreover, while an electronic audio amplifier made with modern components can be made perfectly neutral when terminated on a resistive load, i.e. it can reproduce any input signal without any changes except amplification at its output, once you connect loudspeakers at its output the amplifier-loudspeaker chain is no longer neutral, i.e. it no longer has a flat transfer function between the electrical input and the sound output and it is not at all clear which should be the output impedance of the amplifier as a function of frequency to ensure the least degradation of the sounds in comparison with the input signal.
So it may happen that a vacuum-tube amplifier - loudspeaker system has actually a better overall fidelity than a typical audio amplifier that was designed to demonstrate a much higher fidelity on a resistive load (because thus the transfer function is easy to measure and correct, unlike the complete transfer function to sounds).
In theory, one could make a modern amplifier reproduce any quirky behavior of vacuum tubes, e.g. a higher and frequency-variable impedance or certain kinds of distortions, but usually nobody bothers to do this, because it would be expensive and the normal amplifiers are good enough for the majority of people.