Expanding questions about tubes in a preamp

Skeptics say anecdotal, audiophiles say empirical. 

geoffkait :
I enjoy your post very much and over the past couple of years have learned a lot from them.  But, you have a nasty demeanor.  Why is it acceptable to verbally assault others?

Hope I'm not putting words in @mulveling mouth--get a tube preamp that uses a better tube. I've never liked preamps with 12AX7s--the timbre seems off and dynamics seem non-linear. Hard to be sure, though, as it is the whole system being listened to, not just the tube type. In the preamp alone, there is the circuit, its parts quality, its layout, its build quality, and its output impedance match (or not) to the amplifier input. Add the source, amplifier, loudspeakers, cables, and the room and who knows? Even with something like the BHK preamp which uses either tube, there is still the possibility for optimization for one or the other.

Gents, how the hell does adding damping rings change the sound of a tube. Nonsense!

Answer: by reducing microphonics. The effect is easily measured and heard.

But using a low microphonics tube is more effective yet. Installing dampers on them has the most effect.

Like most topics here, some synthesis required...

yes ALL tubes to some degree ARE microphonic. Some less so than others- certainly a classic case is the 6922 vs 6DJ8.  The key is how much and what are the modes?

The various products vary of effectiveness as broad band dampers.

microphics you can’t hear can still consume power and inject noise in a wide bandwidth system and turn into artifacts you can hear.

Start with great tubes - @bdp24 gave you good advice - Roger Modjeski ( RAM ) built some great testing and grading equipment and knew how to use it. Andy at Vintage tube also knows his way around killer but let comprehensive and automated test equipment. He can be trusted :-)

Dampers can change the sound - you may not like it. You  should experiment :-)