MHDT Orchid or Lampizator Amber 3?

Which 6sn7 do you have?
Modern production of vintage?
Try Ken-Rad vt231 black glass from 40x. They are great and not crazy expansive.

50'-60's Marconi's

rx8man

You may be much more technically savvy than me, but I just looked up the specs on a 6SN7 tube and compared them to the 396A tube. Whereas the specs for a 6DJ8 appear to be pretty equivalent, unless I am reading things incorrectly (which could very well be the case!), the specs for the 6SN7 appear to be quite different. Maybe no damage to the dac would happen, but  I wonder how those differences in specs will impact the sound.

Do they support 6SN7 tubes with the proper adapter (Garage1217)?

In all our dacs, tube is acting as a buffer.
So, the tube is a passive compnents in circuit and so a fixed set up (bias). No needs to adjust resistors’ value for most tube.

However, the tube is working on -17.5 to + 17.5 volts, quite a very low voltage in tube’s world.
5670 can works on this low voltage because 5670 was design and developed for minitary communication equipment during WWII. So, it can be work on hardest enviorment such as low battery source and hard vibration. All pencil tubes were designed to be used in air plane, they also have same characteristics like 5670. 6SN7 is a commercial tube, it may also works on our dac but sound must be another issue.

Best Regards,
Jiun
Mhdt Lab

Subjective/anecdotal impressions would suggest that 6SN7 tubes do indeed work.