Describe ube sound vs solid state

Tube guy: only tubes sound good

SS guy: jump on the transistors, tubes are the pits.

Where is the truth?

Where it almost always is. Somewhere in the middle.

Myself I choose to shy away from tubes whenever possible. Too many headaches. But I still have some. Go figure. I'd love to ditch them all but at least the ones I have sound good plus of course tube gear is way cooler than not and you can't roll transistors to get the sound you want, but there are many ways to tweak besides twiddling with tubes.

^It works the same in both directions, and global feedback is not neccesarily a prerequisite.

If the output impedance of the amp is low enough then feedback is not required. An example is the Ayre amplifier.

An example of a tube amp that acts as a voltage source is a Mac 30 from 55 years ago.

^I'm not familiar with the Mac 30. If that were the case, why would it have multiple impedance taps?
http://www.roger-russell.com/amplif1.htm#mc30

^^ If the impedance of the speaker is too low the output power of the amplifier will be lower and distortion higher. The lower impedance taps are provided to deal with this.

It might interested you to know that the voltage rules that we are talking about (http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php) were initially laid out by Electro Voice and MacIntosh back in the days when tubes were king (late 1950s).

^Them it would appear that the Mac 30 is not capable of adapting to the variable impedance swings of typical loudspeakers without deviating from linear frequency response?