Expanding questions about tubes in a preamp

Uh, they’re all microphonic, even the ones that say ultra low microphonics. I used to get all my 12AX7s and other tubes from an insider who worked in maintenance at Goddard Space Flight Center, they were all WA military grade tubes. Sylvania, RCA, mostly. The only tube dampers that actually work and don’t hurt the sound are Herbies tube dampers. The rest of them you can throw in the trash. On 6SN7 tubes you should realize even better performance by using two, two dampers, one on the glass where the getter is located and another on the tube base. Yes, I know what you’re thinking, “but then I’d be spending more for dampers than I did for the tubes!”

Herbies tube rings are the only way to go the others over damp the tube and you loose life and dynamics.

if you buy into the tube damping thing, may as well go big
https://shop.mapleshadestore.com/Standard-Tube-Halo_p_1268.html

I use quiet  tubes, and I'm done with it. Careful, the more you learn, the more it increases unnecessary obsession. 

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.