Hi there, welcome to the club!
You can search auction sites for the crème de la crème Mullards. Just make sure the seller posts the test results and has 100% feedback, of course. Here are some details you need to know about Mullards you're looking for:
- Can be designated as a 12AU7, ECC82, or CV491
- Made in the Blackburn plant in England during the 1950s
- Construction: 17mm long plates, has a square getter or O getter on top
- Date code: K61 (also, you can look for K62 versions, which were made after)
When I search auction sites, I just search "k61 tube" to lasso in the most listings. Some people like the CV4003 or other types, but most collectors, including myself, have found the k61 really is the very best of Mullard 12AU7 tubes. It sounds closer to an octal type than any miniature tube I've heard: it has a big, effortless, tonally rich, and natural sound.
The Mullard you got may be good, I haven't heard it...Let us know. It's a new-production tube and was made in Russia though. Mullard is famous for their made-in-England tubes from WWII-era and the 1950s, so if you can deal with the prices, it's worth having a listen
while they're still available. Because, obviously, these older tubes aren't being made anymore and will eventually become extinct. In that sense, we're lucky we live in this age to be able to enjoy them.
Some other options:
- Amperex 7316 Long Plate Foil Getter (also rich and warm, but not to the extent of Mullard, also pricey)
- RCA 1950s long black plates square getter (also rich and warm, more rolled off treble, can be found significantly cheaper)
- Raytheon, RCA, Ken-Rad, National Union, Tung-Sol 6SN7GT [using a 6SN7 to 12AU7 6.3V adapter] (WWII-era octal tubes that have nice bloat in the upper bass and lower mids compared to most 12AU7 types, RCA and Raytheon can be found significantly cheaper, the Tung-Sol is the other consensus holy grail tube like the Mullard that sounds wonderfully natural and easy to listen to but is going for insane prices these days)
- Use a 6AS7G type output tube (I've found this has a more drastic change on the sound compared to input tube rolling, input tubes can slightly color the sound better though, the 6AS7G is warmer and more spacious sounding in my experience compared to 6080 types)
Be warned this obsession has become a black hole for many of us. Perhaps, you'd be best served to just take out the Speedball, if you loved that sound already... Cheers
