Expanding questions about tubes in a preamp

Getting rid of microphonic tubes is far more important than damping rings. They have a tiny effect by comparison. I would only use them if you already have decent tubes.

Heat in tubes causes failure. The more damping rings and the like, the shorter the life.

I've had tube preamps that were too noisy for my system's downstream gain structure (both rush noise and microphonic feedback), and no amount of super special tube selection or tube dampers or HRS damper plates or expensive isolation stands did jack about it. Certainly, once you get "Platinum" selected tubes from Upscale Audio, there's not much (if any) improvement to be had from better selection. 

You have to pick a preamp with reasonable gain for your system and good signal to noise ratio. This is one measurement you can glean from Stereophile reviews that actually matters - for example, see the ARC Reference 6's 100dB signal/noise, which is excellent for a tube pre, and tests in my difficult system bear this out.

BTW if your line stage uses 12AX7 and EF86s, those are NOT typical choices for a modern tube line stage. 6SN7, 6922, 6H30 seem to be preferred (also in my experience). Though with the old 6SN7GT types, it is HARD to find quiet examples today.

Gents, how the hell does adding damping rings change the sound of a tube. Nonsense! If your tubes are microphonic (ringing) adding dampers may quiet them down. If you have a noisy tube it won't help. But it also won't hurt. I have never heard anyone complain about, nor have I noticed, a change in sound due to the use of tube damping rings.

Using rubber bands as tube dampers? Sure, go ahead. As long as you don't mind smelling cooking rubber and the bands sticking to your expensive tubes, then cracking and falling off. Rubber bands are not designed to be heat treated.

Next silly suggestion: why not just coat your tubes with a healthy dollop of undercoating? It made my '67 Bug quieter.

... Phew! - this is getting more complicated - may have bitten off more than I can really manage at the moment...

Thanks to all for obviously educated and experienced info.

Hum is either a design or installation fault.
Hiss is a gain structure fault.
Microphonics are a tube fault.

IMO, chassis damping has more effect than tube dampers.

I first used VPI blocks on my Citation II in the late 70’s/early 80’s, whenever they became available. Blew me away. Been collecting more ever since.
Ditto support damping as seen here
http://www.ielogical.com/assets/M-125/VPIBrickDamping.jpg

NO ONE has ever failed to hear the difference!!

@OP - why such a cryptic topic?