The musicality of the "tube" sound is a real phenomenon. It has long been known that listeners appreciate the addition of a certain amount of second harmonic distortion, and tube amplifiers produce just that, due to enormous difficulties in maintaining good linearity with acceptable feedback coefficients.
While this distortion may sound nice, Hifi is supposed to be about precision, and if the sound needs to be altered in this way: it should be limited to a front panel adjustment of the pre-amp or integrated amp, like "Smooth Old Sound: ON/OFF".
Tubes offer some advantages - their overdrive behavior is smoother than solid state, so even when clipping the sound is less "harsh" (even harmonics). While this is desirable for a guitar amplifier that runs on distortion most of the time, it is of no use in Hifi, where distortion must be completely avoided.
Tube amps also (usually, but not always) have a much higher output impedance than solid-state amps, which makes some speakers sound better and others noisy, so results are unpredictable.
In fact there are very few tube amps of any cost that will outperform a very basic modern transistor amp.
Indeed, the vast majority of transistor amps are so superior in every way to any tube amp, that it is hard to justify the use of tubes in anything other than guitar amplification, where, despite lots of marketing hype: no transistor amp has ever been able to sound exactly the same as a tube amp...we're getting close...but it's not the same.
The appearance of monoblock class A triode tube amplifiers ... is truly amazing. They typically have abysmal 1-5% harmonic distortion at rated rpm, are low power (typically less than 5W continuous), not to mention the wear and tear/planned obsolescence of tube technology. Such an amplifier generates large amounts of second order harmonic distortion and requires a very large output transformer. The distortion inherent in the iron-core transformer is ubiquitous, and only violent feedback can eliminate it. Significant feedback around a transformer is extremely difficult to achieve correctly, as phase irregularities usually cause the amplifier to oscillate....
In summary: it may have been the state of the art 50 years ago, but there is no valid reason to use tubes for high fidelity amplification: as long as we know why not praise the virtues of wax cylinders or vinyl... as having a sound superior to the CD, LOOL 😅
Below is the typical form of reproduction of a "square" signal by a very good tube amp, at 100Hz, 1000Hz, and 10KHz, I let you judge the massacre...
Recently in a review I saw an amp over $2800, a class A triode thingy advertised 4% THD at 10 watts....which is absolutely appalling for an amp...even low range: most powered PC speakers do better than that!
I have no doubt that many tube amps have a very smooth, not unpleasant sound... it's not Hifi, but I must admit that I do like Lowfi, from time to time. ..
