Expanding questions about tubes in a preamp

So just putting some rubber rings (O-Rings) picked up at a local hardware store would not be a good idea - or is it just again an experiment worth trying?

Better than paying for Herbies. I would try one per tube that fits snug (not real tight) and also a couple sized bigger. The big ones will let you shim or slide something between the o-ring and the tube. This will let you experiment with the vibration control effects of different materials- wood, paper, metal, whatever you want. I doubt you will find anything that does what you're looking for, but at least this keeps the learning costs down.

The RAM Tube Store meticulously measures all tube parameters, including noise. They then grade each tube, and offer matched pairs and quartets. They offer a Super Low Noise 12AX7's for use in phono amps, etc. A very quiet 12AX7 substitute is the 5751, which provides slightly lower output.

insearchofprat OP
Expanding questions about tubes in a preamp

First weed out any mircophonic tubes.
Do this by turning up the volume to where it sits normally for loud listening, get someone to gently flick each tube with his finger nail while you listen at the speakers for the bad ones. A quiet "bonk" is ok, loud or a tinkle behind the bonk (tinkle can be very loose stretched heater filaments) or sometimes when real bad you'll get run away feedback, quickly turn down the volume..

Once you have a batch of good non microphonic tubes in, then these cheap red "O" rings the thick ones, two per tube one high, one low not too tight. I have seen power tubes get a dent around them when they were too tight. (don’t bother with expensive audiofool tube dampers).
https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2334524.m570.l1313.TR5.TRC2.A0.H0.Xsilicone+%22o%22+rings.TRS0&_nkw=silicone+%22o%22+rings&_sacat=0&LH_TitleDesc=0&_osacat=0&_odkw=Red+silicone+%22o%22+rings

Cheers George

Hi,
i would suggest to experiment with Herbies tube dampers, check them as there is variety of those, and not loose their grip or pressure on the glass over time. Silicon or rubber ones do work somehow are cheap but get loose or crack after some use due to heat. Whatever you choose will do in vibration control tame microphonis and make your tubes sound more linear if you want that. What i have found is that putting them on the upper part of the envelope, above top mica, is less affecting the tube character.

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!”