The Run Down on 12AU7

A cousin of the 12AX7 tube is the 12AU7 and just like its cousin there is a small commodity of the premium vintage versions of it left. Other versions of 12AU7 are 12AU7A, 6189, ECC82, and 5814. It can be used as a class A amplifier per triode section, preamplifer stages of high fidelity audio equipment, musical instruments, public address equipment, and broadcasting equipment.

12AU7/12AU7A- The most commonly made in the U.S. and RCA, GE, and Sylvania manufactured the most of them here. It seems like everyone wants to get their hands on the RCA 1960's version with greyplates and the getter on the side which became known as "cleartops." Although the earliest version RCA made had ribbed flat blackplates with a top getter and a white label. In the 1970's there was a RCA new logo version with a white label, like the 1940s+50's versions, greyplates, and a top getter.GE pretty much kept their model the same throughout the years always have greyplates, a topgetter, and numbers carved into the glass with a connect the dots looking pattern underneath. Tung- Sol made this very cool looking and very rare "blackglass" version in the late 1940s, like throwing tinted windows on a car you cant see inside. They changed that design later to resemble early RCA's with greyplates on the inside, yawwn.

ECC82- This is the identical European version. The run around as 12AX7 the in demand brands are Mullard, Telefunken, and Amperex. The rare Telefunkens are the smoothplates but there is also ribbed plates and all of them have a diamond shape molded into the bottom of the glass. Amperex most popular tube is the buggleboy with the logo of that little tube dude blowing a horn. Later the label goes to white with just the words "Amperex" and after that a orange logo arose with the world logo. Both Mullard and Amperex have put on your glasses small date codes etched into the bottom of the tube. Mullard longplate versions that came out in 1950's are the cream of the crop of this brand in 12AU7s, their plates were 3mm longer than the 60's versions. Some of the earliest had square getters and the later ones had halo top getters. The earlier Mullard logos just said Mullard then the later ones said IEC Mullard. Mullard and Amperex one day got together and made a baby just for the military called a CV491 longplate with a square getter.

5814- You can tell by the number code that it was a military spec tube. GE and RCA made these for broadcasting in the RCA command series and the GE 5-Star series. All of these have low microphonic because of their mica supports and a rare one to get a hold of is the "triple mica" versions. Very durable tubes and most have 5814 etched into the glass except some GE's have 1G-12AU7WA in white on them.

6189- When you can find these they are great. GE also put this tube out in their 5-star military line. Usually the military version will have 12AU7WA listed on the tube as well as 6189. The RCA version has 12AU7WA written in gold with blackplates and extra support rods. The older vintage versions also have blackplates and a "triple mica" spacer at the top.

6680-Just like the 12AU7 but it can withstand filament voltage variations without affecting its output. Originally used for two way mobile radio use. Motorola and GE being the most common to find today but there is also a rare RCA cleartop version.

ECC802-A premium European version of the ECC82 that has matching triode sections and is as rare as the bald eagle in the U.S.

B749- Another extremely rare one in the U.S. It was made by Genalex in the "gold Lion" series and has the gold lion script in gold on the glass.It also has a red Genalex decal across the bottom and has a grade A repuation for sound so as you can imagine top dollar.

Lets hear more about how they sound!

Telefunken and Siemens- Breath taking open air, t-rex large soundstage, great for adding some spunk to mono apps, the midrange is like it just got ran over by a steamroller it's so flat, and a on point bass . They can be found on the brightside though.

Amperex, Philips, Mazda, & other Holland/France New old stock tubes- does a balance of justice with a clean airy top end, the midrange has warmth, and again the bass is on it's A game. Recomended for musical uses of hi-fi equipment. Unusual for alot of European tubes these break up great when overdriven in guitar amps. French Mazda combines some of the more warm sound you get from amperex with the air you can get in a Telefunken with a dynamic punch in the sound.

Mullard & Genalex-warm midrange, the top end could be described as milky, specialize in making human voices exspecially female voices feel as if there was a ghost standing next to you singing, definately has razor sharp detail.

RCA, Raytheon, GE, Sylvania, & more USA made NOS-I recomend the RCA, Raytheon, and Sylvania blackplates out of this catergory because they are very musical and have a sparkle of air at the top end, warm midrange, and slamming bass. The RCA are great for guitar amps even in greyplates and longplates. I have heard GE greyplates called "all around nice guys" too bad nice guys finish last.
　
Remember that all vintage tubes producers used a chalky label paint so often labels are smeared which virtually doesnt mean anything although could be taken for poor quality when they have enver been used.