What made you change to a 6SN7 preamp?

I was immediately struck by how much quieter it was, how much detail it had, and how it presented as good or better of a soundstage and had very precise imaging. 

It would be lovely if we could attribute the characteristics above to a particular tube; we could all just use that tube and then have state of the art. To address those characteristics has everything to do with operating points, bandwidth, parts quality, grounding, layout, power supply design and so on. The advantage of the 6DJ8/6922 is its linearity and bandwidth (it was used for instrumentation for example) so if you have a non-microphonic tube you'll do well. Since microphonics was not a concern in the applications for which this tube was designed (like television tuners) finding non-microphonic examples is a bit of a task.

Without naming designers, one shared with me he decided to use either 6DJ8 / 12Axx instead on his next version preamplifier because he felt the availability of good 6SN7 supply was dried up or hoarded away. That was 4 years ago.

Today we see more new production and updated 6SN7 / CV181 tubes showing back up from across the pond, more people testing them out, all hoping they last longer than a year or longer than any of their NOS stored away. I'm on that list myself. Not sure how this may or may not influence component designers moving forward. 

I continue to learn a lot from this thread. Thank you all so much.

@big_greg There's a Herron preamp listed used that I have my eye on....someone stop me before I ruin a perfectly good marriage.

Thus, a question which controlled for this would ask whether your change in preamp was lateral in terms of construction quality and nevertheless there were improvements in sound which could safely be attributed to the tube?

I upgraded my 6SN7 ,preamp to another 6SN7 based preamp. It was a true upgrade in sonics, but one aspect remained constant, I heard the same characteristics that a 6SN7 provides. Rolling tubes used in the first preamp presented the same type of textures, imaging and soundstaging. There were, of course, many improvements in detail, noise floor, dynamics, and realism owing to the superior quality of the new 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.