Tube imperfections

I haven’t used a 5670 so I can not comment on your question if there’s a sound difference between JAN/2C51 marked WE396 to one just marked WE396 . If you are unaware of it, there was an Orchid DAC thread that possibly has some discussion about that; if not it will afford you identification of some members that own the Orchid that you can possibly pm to get some direct insights.

" I realize that audible variations may be hard to hear at the DAC level so there’s that. " I have a Modwright Elyse DAC in my 2nd system; I can tell the sonic difference between Phillips, Siemens and Mazda 6922s in that DAC . You do have some options between variants and brands 5670, 2C51, 396A, 6385, 6CC42, 6854, 6N3, 6854, CV2575, CV4013, CV5894, CV8247, CV2381

I have not found glass warping to be "common" with small signal tubes.

MC, that seems logical in that it's a vacuum after all and the electrons and current activity would seem to be based on simple distances, parallel plates etc.  OLDHVMEC, indeed one of the equivalent valves I'm curious to try is in fact a Russian military 6N3P-DR and it's currently in the unit getting some break in time before I A/B it with the WED396.  FACTEN, it's good to hear that some, and with their systems, can hear the differences.  I don't think or want to think, that this denotes a bad tubes or good tubes  but one that a person simply likes better than another. That's the hope.  Whether or not it becomes a white whale I doubt but winter in 2020-21 could seem long and there's no telling how obsessed one gets!  I combed the AG threads for my short list but was thrown by this on the two first tubes I try.  I just might try another vendor as these aren't that expensive.  

I can just about guarantee there are differences you will be able to hear if you listen for them. You will probably also find some that make a big enough difference to be obvious. You might even find one that is so obviously better it was worth the money. But I can also just about guarantee this will not happen on the first try, if ever. Almost always what is much more likely is you will go through three or four modestly different results, just enough to tease into keep trying, maybe after four or five you get one good enough you feel maybe this is all worth it, maybe this next one....after a while it starts to seem you're getting closer and closer wow these tubes really are distinctive. 

When really what is happening is you're getting better and better at the fine art of discerning differences between tubes. So that if one day you do find the white whale it really will feel like a white whale. Even though at the end of the day the difference between the very best and the very worst of them all is less than one $160 Synergistic fuse, only you had to spend five years and $1500 to figure this out. This being more cognitive dissonance than most can stand you inevitably decide it was all totally worth it. And round and round we go.....
Another thing you might learn along the way, which nobody mentions, is instead of tube rolling you could be diode rolling. Because, let me tell you, there are massive differences between diodes. They cost a lot less. Changing them pays bigger rewards by far. And its just about as much of a crap shoot. But it calls for soldering skills. So nobody does it. Otherwise for sure if someone ever invents a diode you can just plug and unplug then by God audiophiles will all be into diode rolling. 

Oh wait- tube diodes! Nevermind! lol!
https://www.youtube.com/watch?v=K0gSNTAA0_Y

I have the mhdt in a second system and find the 6n3 comes across with a nice cleaner sound thank the GE or WE. The strange thing is and I may try it is to get tube adapters ($25 very nice quality) from Garage 1217 web site and run 6922 or 6sn7's. I have a huge stash of very nice NOS 6922, 6sn7 tubes. Check out Head-Fi web sight on preferred tubes for the mhdt. Many run the 6sn7 and 6922 which I would think is a much better tube than the funky 5670 but it does sound good so going with adapter may be a waste of time. I've not heard of mhdt going up in flames using adapters.

MC, thanks for that!  In regards to diodes I shouldn't doubt you but one thing at a time.  I'll stick to a tube or three and just select the "best" given my ears, the way it works in my overall system.  You had to mention the f___ word.  Here we go!

paulcreed, indeed I've picked up on the adapters and the new list of tubes that it opens up.  So far, my first impressions of the 6N3 is similar but to MCs point, different often comes across initially as better but time and repeated A/B will tell.