Best 12AU7 Type Tubes for a Preamp

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.

I've never been impressed with the RCA clear tops...or Mullards for that matter. The best I've heard are the German tubes, be it Telefunken or Valvo or whatever brand got stamped on the glass. The labels are meaningless for most NOS tubes and the codes should be used to evaluate where they were actually produced. The tubes that came out of Holland are very nice sounding, if a bit "sweeter" than the German stuff. Phillips had tube plants all over the place and they often weren't all that particular about what brand came from which plant. Tung-Sol produced some really nice sounding, smoked glass 12AU7 tubes that rival the European stuff, but are very hard to find and easily worth the extra scratch. 

In short, the German stuff is the best and worth the money no matter what brand is on the glass. The Holland made tubes (usually Amperex, but code specific) are very nice and sweet with good detail and worth a premium, followed by European tubes in general that were manufactured by Phillips. Mullard is distinctively warm sounding and often flashes when first powered up. American NOS are hit and miss across the board, with the exception of the Tung-Sol tubes that were terrific. Of the American brands, seeking out the military and commercial radio designed variants are the way to go. 

Thanks all - you have offered some really good thoughts and suggestions for me to consider, and thanks @dekay, the linked thread did have interesting and useful information.  

I live about an hour from Andy Bouwman • VINTAGE TUBE SERVICES, and I can get up there almost any time I want for my work so there would be no need to ship tubes.  I purchased from him long ago so I know how meticulous he is, which means higher prices, longer lead times, but almost surely a more successful result than dealing with mass market type sellers.  Since I only need two tubes, I plan to call him on Tuesday when he is next open and then purchase whatever he recommends.  As a bonus, there is some really good mountain biking very close to his shop!

As a last thought, this thread has reminded me of what a helpful, friendly community we have here - thanks again.

@mitch2  - Below is the link to Brent Jessee's website page for 12AU7's he gives impressions of the sound of different NOS 12AU7s which may help you match the tubes with the sound signature you prefer

https://www.audiotubes.com/12au7.htm

This thread got me thinking about a pair of Viking RP61 tube preamps that was given to me from an estate some 20 years ago. Also included was a McIntosh MC240 amp and a MC20 preamp. I was given a nice Kennedy tool box with quality tools in it too so the fellow had good taste to say the least.

Anyway...the Viking`s were stuffed away until a couple years ago. I finally opened them up and ended up with a pair of Amperex Bugle Boys 12AU7 made in Holland with D7H printed on each of them.

I`m thinking I`ll bring them with me when I visit my daughter and son in law to try in their Rogue Sphinx II. Might be interesting to see what kind of change they make to the sound.