Tube Amplifier Sound Characteristics

BTW since I have heard the VTL and like their sound I would buy one on the used market except that only the really old ones are available and I am willing to spend more to get something not too old.The ASL are nice sounding but poor reliability from what I have seen. My tech advises against it.
I like the ARC but one owner tells me it is on the cool side, a bit bright and edgy.

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.