Not always, but sometimes. IIRC, Eddie Van Halen’s characteristic sound came from a particular Marshall amplifier with a few cheap MXR bran effects boxes, and the amplifier played very loudly. I recall an interview in which Eddie said that he liked to be able to feel the hair on his arms move from the sound. How he has any hearing at all left is beyond me.
Even if you aren’t cranking the amp to eleven, there’s a distortion you get from tube amps that shows up even at lower volumes. A lot of people (myself included) like the way this ends up making the guitar sound. If you run music through an amp like this it sounds like crap, but for a guitar it sounds good.
Most of the guitar amps I’ve looked at haven’t used negative feedback.
There are effects boxes that do exactly this. There are also very complicated digital effects processing units that can simulate everything from the unique distortion of tube amps to the effects you get from old fashioned spring and plate reverb units, and even the peculiar echo effects you get from someplace like a concert hall (which is not a simple delay echo). Units that do this well are very pricey. The el-cheapo effects boxes you get at ye ol local music store just don’t cut it. An overdriven cheap tube amp has a “good” sound that is difficult to replicate without expensive equipment.
You betcha. If you really get into it though, you find that while the explanations you get from some folks is really wonky, there is something to the particular sound that they are describing.