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.