Back sometime in the mid ’90s, one of the best audio investments I ever made was retubing my 12au7 Cary preamp & my 6922 ARC amps via Andy at Vintage Tubes. He sold me a half dozen NOS Mullard 12au7s for the preamp, and the years that I ran that combination made for some of the best sound I have ever had.
That was a long time ago, however, with different amps, and my ears were a lot better, and I believe the room was more friendly than the one I am in now. About four years ago I bought some French 12AU7s (I think Cifte was the brand?) from Uncle Kevin at Upscale, and I did appreciate their sound, but things have never been as good as the way I felt about the equipment with Andy’s tubes. But I do need to defer to the disclaimer about amp & room & ear changes over the past 25 years.