What made you change to a 6SN7 preamp?

Bought a used Ultraverve pre here on Agon, compared it side by side with my highly reviewed, more expense 12AU7 pre. Immediately sold the 12AU7 pre. Soundstage opened up, instruments and voices sounded more lifelike to me. I realized it was the sound my system was missing. Kara of Dehavilland built me a Mercury III and I rotate the two pre amps. I learned from this:1) more expensive is not always better 2) you can’t know what you are missing till you try it as it may be the sound you want 3) the preamp has a HUGE impact on your system. I am not saying 12au7 pres are not good, just sayin for my ears I like 6sn7 much better.

@atmasphere Ralph, I think you were reinforcing the point I was trying to make that it's not all about the tube?  Interesting to hear the 6DJ8/6922 was intended for use in TVs.

@hilde45 I don't have any experience with the Quicksilver preamp you have listed in your virtual system, but I think you'd find the Herron preamp a night and day difference.

@lowrider57  Thank you for relaying the story about that upgrade. It bears on my question directly. Very helpful.

@moofoo  Your example, too, bears on the question. And as others have said, there's no substitute metric for actually hearing it. Expense, tube, design are all relevant to the question, though. 

@big_greg  Thanks for your comment about the Herron. I need to sell something before buying anything else, but I'll keep my eye on that Herron. My Quicksilver got upgraded with Mundorf and Vcap caps and sounds pretty good. A night and day difference would really be the reason to change.

There are lots of possible tube to use. My favourite preamp uses 6GK5s.

I think you were reinforcing the point I was trying to make that it's not all about the tube? 

That is true. But if you work with tubes over time, you get a feel for what they do. More to the point though that in order to really compare what the tubes do, you have to make sure all the other variables (circuit topology, part quality, grounding technique, power supply design and so on) are put to bed.

We see this going on in the SET world all the time- SET fans say they've compared SET to Push-pull, but when you dig into it you find out that the variables I mentioned above were uncontrolled in the comparison. This makes comparisons invalid; all you can conclude at that point is you might prefer one over the other without knowing why that is if you're being truthful with yourself.