I've heard transparent tube amps, back in the late 60s. But I agree, the "tube sound" is pretty intolerable. I didn't like it growing up, and I don't like it now.Serge years ago said that a well designed tube amp could have extremely low distortion but then itwould sound just like a transistor amp.
My experience with valves apart from the fire hazard and inherent unreliability was the syrupy sound just awful.
Perhaps if you only listen to solo female voice but even then.
Keith
Being cynical, I could believe the syrupy sound was a useful bandaid over the sound of some old speakers.