Tube Amplifier Sound Characteristics

Doesn't the "sound" of a tube amp depend on the various tubes involved?

If there was going to be a Venn Diagram, it would have to be at least two Venn diagrams -- one comparing different amps with the same tubes, and one comparing different tubes with the same amp.

How much feedback is being used. What do you know about the transformer windings. I know some from a certain country do about 6 windings. With a machine. Terrible frequency characteristics, but hey, it looks pretty.

Once you are satisfied with "basic" build features such as these and perhaps others will become relevant - tube rectified? choke, any ICs, SET or push/pull, cathode/fixed bias? etc. (SE *may* mean its a SET).

Then what tubes? 300B are a very different beast than EL34s, for example (try to stick with popular tube types such as these).

Other things you might ask about, to get an idea if the vendor has more than 3 neurons - is it a triode, ultralinear, pentode or other type of amp?

I know nothing about brands that come out of a factory.  Mine was handmade by an artisan.

Be informed.

There are a lot of variables in play....the circuit, the caps, the tubes, the rest of the system...all contribute, so even an amp of the same brand and model can sound different with different tubes.  One of the things I like about tube amps is that you can tailor the sound to your liking by carefully choosing which tubes you use.  

+1 @knotscott  Spot on. Sort of makes most of the threads debating about amp brands look suspiciously like a waste of time.

@Hilde45 I was just thinking of tubes as supplied from factory or stock units. For example on the extreme left (warm/tubey) I find Conrad Johnson. I have a Rogue preamp that is more in the middle. I have heard from people that in general that is their house sound.