This is a dicey topic. As we have said, it’s like telling you which red wine you will enjoy the most tonight with dinner. How would we know?? We don’t, really. All we can do is share what has worked for us, and what we hear from others that we have been able to validate.
First, a quick note: there are many tube types that are equivalent to 12au7 tubes. This means they can be used interchangeably with 12au7 tubes. For example, in Europe, most 12au7 tubes were called ECC82. And the 6189 was a “military grade” 12au7 tube. There are many more examples.
Here are some NOS 12au7 tubes (and “equivalents”) that we have found to sound especially good:
- RCA 5814A black plate triple mica (all-around musical and very pretty)
- Mazda, 12au7 and 6189 (wonderful space and detail, really delivers “the whole sound”, perhaps slight emphasis on mids and highs)
- Amperex “bugle boy” (just an incredible tube, slight emphasis or spotlight on those female vocal frequencies)
- Amperex non-bugle boy, but should be made in Holland, early 1960s or older. We have not been “wowed” by the newer Amperex tubes with orange ink. However the early pre-bugle-boy Amperex are even better than bugle boys… unfortunately they are incredibly expensive
- Mullard, made in Great Britain — however, there are many different Mullard types that work as a 12au7 and we have not come to a definite conclusion as to which ones are reliably better than others. Some Mullard tubes can sound a little too warm and congested, or lacking “space” while others are just absolutely brilliant, to-die-for tubes.
- For an especially neutral sound that is very correct or “flat” in terms of frequency response, Telefunken (although we have found that in some but not all cases these can be so absolutely neutral-sounding that they sometimes do not convey emotion as well as other NOS tubes… also, Telefunkens are often “crazy expensive”)
- RCA clear top (excellent bell-like clarity with very good sense of space, although gut-punching low bass and mid-bass may be slightly lean… perhaps for this reason, these tubes can be more affordable among the many NOS options)
- Valvo (love these German tubes… because they are excellent at conveying emotion, we like them more than Telefunkens, which is fine because Telefunkens are usually more expensive… however, Valvos are relatively rare / difficult to find. They were often made by their parent company Philips in Holland instead of the German plant… still great though)
Please note: as we explained at the end of our article “Do NOS tubes sound better than current-production tubes?“ the above tubes, like all NOS tubes, have various disadvantages that you should be aware of.
Good luck!
