Tube amps

[Hatingmusic]

Why is the overdrivven sound from the tube amps is called the sweetest, warmest?

[Jazz P Bass]

My two cents.
The tubes 'compress' the sound.
Plus the output transformer 'adds' it's own character.

[J M Fahey]

Agree and add: many classic Tube amps (think Fender Twin or Super Reverb) , used at around volume "6", are already clipping, at least part of the time, yet the natural tube compression does not let such distortion go too far, and sound, in a "live" setting (with other instruments plus drums, and in a big reverberant space) is perceived as "clean", although I have personally hooked a scope at speaker terminals and clearly seen some distortion on peaks.
A typical SS amp at same settings will also be clipping, no compression at all so the signal "hits a brickwall" and the sudden clean-to-clipped transition *does* sound harsher.
The tube "brickwall" is also there, but it's "cushioned" , so to speak.
And yes, the transformer saturates on its own, in a softer, smoother way.
So yes, there are real differences between Tube and SS clipping, although with careful design SS can reasonably copy Tubes.

[Chuck H]

Agree and further add... There's a whole bevy of little differences too. Tubes usually work with a shifting voltage supply where SS devices are regulated. This alone makes for many differences as it applies to guitar amps. Tube guitar amp ciecuits usually employ much less NFB than SS amps. This make's different dynamics. So, looking at tubes with just these two considerations, there will be a more dynamic attack envalope and the amp will have a greater reaction to these dynamics. That's a bunch of stuff going on that is very real but hard to quantify. Since one little thing is little, but a bunch of little things can make a pronounced difference. Along the same lines, it's also true that there are many different tube designs and they are all different in how they present these qualities because tubes offer a wide range of operating parameters. The list goes on and on.

[soundguruman]

Transistors are imitation tubes.
They are OK for telephones, but not music.

[Chuck H]

Transistors are imitation tubes.
They are OK for telephones, but not music.

I don't think they're "imitation tubes" so much as different amplifiers. There are many things that transistors can do BETTER in guitar amps than what tubes were historically used for. Reverb, effects loop, summing stages and almost anything that requires re amping come to mind right off the top of my head. And there are a great many coveted guitar tones that can be attributed to stomp boxes as much or more than the amp itself. Those are all SS devices. So rather than taking the stance that tubes are better (though so far they are for me) I'll just say that tubes and transistors are different. But to address the OP...

The only criteria in post #1 that seems to qualify tubes as superior is the term "warmer". A very subjective term. Warmer, to my mind, simply means less top end, more bottom end or both. This is achievable with EQ. So a more in depth discussion is probably warranted. However, given the great difference between the amplifiers in question, and the fact that a good SS device sounds better than a bad tube device and vice versa, we can only discuss the relevant operational differences. We are only starting to come into an age where SS device amps are being manipulated to behave more like tube amps. This effort is being swamped by digital technologies though. So a more complete evolution may never see light. And it could be that tube amps are deemed better for no other reasons than tubes were what was available when all the criteria for tone was being developed. The systems we as guitar players use, the guitars and amps, are still much the same as they have always been. Gutars and amps were developed side by side and tubes were the devices used when this happened. There is also the issue of perception. Since tubes, and their characteristics are what we're use to hearing, our perceptions are biased. What if tubes were the newcommers on the block??? My own opinions differ from this stance, but that's not the point.