@amtprod I got the Mullards (and others) from Brent Jesse. Go to audiotubes.com
Brent is a guru, let him know Ian sent you (wont save you or me any money but it would be nice)
Best way to get a hold of Brent is email. He is busy and short handed.
The Mullards were expensive, $450/pair (1950s halo getter long plates).
Brent also recommended "Brimar military CV4035 “flying lead” 12AX7 modified by Bob Hoviland for use in a 12AX7 socket". I think these are $350/pair.
I have relatively cheap Brimar’s in my tube amp and they are wonderful - I’m a/b testing these against a much more expensive Mullard’s right now and so far the cheaper Brimar’s are better but I have many hours to go before making a call - the Brimar’s have a lot more hours on them than the Mullard's.
Dave from Raven Audio also suggested Amperex & Valvo (ECC83). Brent has these and lists all prices and in-stock items online.
These tubes were recommended specifically for the DAC - ZERO noise / microphonics.
Brent will allow a trade-in if you dont like what you get - no re-stocking fee if you apply the full purchase price to another tube.
I’d give the Brimar’s or Valvo’s a try first.