Supratek Cortese--avoiding microphonic tubes

I have put at least 200 hours on the phono and line stages of my recently purchased Cortese preamp. I'm generally quite pleased with its sound so far, and feel that I'm pretty close to getting just the right balance I'm looking/listening for. Just a short while ago I tried my first "tube roll", by substituting the Sylvania VT-231 for the stock Electro Harmonix 6SN7. The Sylvania sounded clear and pristine, (though, to my ears, not really significantly better than the stock EH), but it came across as very microphonic. In doing some research on the net, I've encountered various comments that have included warnings about microphonics, particularly in some of the early, popular 6SN7 NOS tubes. In fairness, these warnings applied to "particularly sensitive" equipment. With its very high gain, I suppose one could place the Cortese in that category. In any event, I'd like to hear from some of you Cortese owners about what kinds/makes of tubes you have experienced as markedly microphonic in your system. There might possibly emerge some kind of consensus regarding what sorts of tubes Cortese owners should be wary of.
You can get a microphonic tube from any manufacturer. With the cost of NOS tubes, you should ask for and receive return privileges for microphonic or noisy tubes. And yes you will be much more prone to this kind of problem with a very high gain unit like the Suprateks. I will tell you that in a CARY amp, I have used herbies dampers to good effect, even on a pretty microphonic Sylvania VT-231.
I second herbies tube rings.
I will check into Herbie's tube rings. Incidentally, the fellow who sold me the Sylvania was very considerate and DID give me a refund. And, yes, Sleepwalker, you are correct, caveat emptor is alive and well.
maybe just been lucky but 5881/6L6s have been more prone (although none that were a big problem unless you thumped the pre)in my Syrah.
Quietest tube pre I've ever owned by a long chalk.
Tube dampers very worthwhile and I also sit pre & psu on FIMs or Dharumas