Positive Feedback ISSUE 44
july/august 2009

Mullard 12AX7 Tubes… Get 'em While They Last
by Robert H. Levi

The 12AX7 tube is the most common 12 volt tube used by everyone! Invented for portable phonograph use in the 1940's, its use as a high output triode grew during the 50's as did its quality. It still lags 8 dBs signal to noise ratio behind the 6DJ8 series, but has higher output. It is made worldwide as a 12AX7, ECC83, 4004, and more. A lower output 5771 also works most of the time, but is not always a perfect match.

I'll cut to the chase. The best of these ever made were the Mullard [Blackburn factory] 4004 made in England. Mullard also made these for other companies including GE and more. Look for the “Made in England” stamped on the tube and that'll be a Mullard. These were made in the 50's through the early 80's, then the factory was closed. I'm told the early production was best, but not to worry. The differences are small and buying them with matched triode sections and low noise will be what you should really be concerned with.

The problem: the world is quickly running out of NOS [new old stock] Mullard 12AX7s! Expect to pay $100 each for excellent quality and more for matched pairs. You can get away with lesser quality matching if used in some line sections, but not for precision use like phono sections. This is a warning: get them now or forget it.

I have tried current 12AX7s by all Russian, Chinese, and Slovakian companies. They are okay, but not as detailed as the Mullard. Even the new Russian Mullard sounds pretty much like the Electro Harmonic's version. The new Russian Tungsol tube is about the same as the new Mullard. The are low noise and play nice and loud, but textural info is limited.

The Telefunken versions are faked quite a bit and don't sound as fleshed out in most applications. I consider them a second choice. The Dutch Amperex pieces are almost as good, but even rarer. Forget about Bugle Boys! That boat has sailed. The Mazda's are usually noisy. The Japanese copies are just OK. You see why most major high-end manufacturers have switched to gear using 6DJ8 types.

I found a good, but expensive stash of authentic Mullard 4004's at Upscale Audio in Upland, CA. Check it out on line. VTV is out of them. They don't even have used Mullards.

Be careful of dealers in Hong Kong buying up used 4004s and washing them, relabeling them as NOS Mullards, faking the boxes, and selling them as new. Get them from someone you trust!

The 12AT7s and 12AU7s are less scarce, but the great Mullard versions are on the wane. Right now they cost about half of the 12AX7, but they will disappear, too!

It's now or never. But a pair or two whether you need them or not. You'll be happy you did. They never wear out unless used… kind of like old light bulbs. New ones will last up to 10,000 hours in most applications so new is best. Consider yourself warned!