A Quick-shot, 3 Tube, 12AT7 Shootout
by Steve Graham
The 12AT7 is not the most commonly used preamp tube in audio. That distinction probably falls to the 12AX7, especially when you add guitar amps to the mix. So why do a 12AT7 (aka ECC81, CV4024) shootout? Because the opportunity arose when I had the Elekit TU-8340VK push-pull power amp in my stereo den a while back. (links 1, 2)
The Elekit uses 12AT7’s for both voltage gain and phase splitting, two for each channel. And I already had three quads -two NOS and one new production – of my own. I wouldn’t have to beg, borrow and test the patience of the kind people who have loaned tubes unstintingly on previous occasions. As these are tubes from my personal ‘inventory’, there’s no time pressure to return them or write the review.
Why three quads you ask? Spares for my DIY phono stage. It’s not ready for prime time yet, so the Ellie amp would suffer yet more tube-change related trauma after the power tube shootout that I subjected her to. Decent NOS 12at7’s are available at reasonable to reasonable-ish prices, likely because of the aforementioned limited audio use. Unless of course, you have your heart set on some Amperex or Telefunkens. Then the prices are, to say the least, eye watering.
A note to guitar players: The 12AT7 is not normally used in guitar amps, the exception being as a reverb driver in some Fenders. This is a punishing job for a 12AT7, and the only one that’s reportedly up to the job is the JAN Philips 12AT7WC. Your amp tech or favourite tube vendor should be able to sort you out.
All tubes under review had at least 120 hours run time on them before serious listening commenced. In my experience the sound of all tubes change, from when they’re fresh out of the box. Some by a little, some by a lot, and almost always for the better.
-Triangle Antal XS speakers, mid 2000’s vintage
-‘Jane’ Aikido 12Vac line stage with a few tweak parts
-Cambridge Audio 840C CD player
-PS Audio Power Plant Premier for AC Conditioning
-My usual motley array of DIY interconnects and speaker cables
-Elekit TU-8340VK power amp, with Takman and Amtrans resistor upgrade, basic Mundorf capacitor upgrade, and Lundahl output transformers. Output tubes: Genalex Gold Lion KT77 reissue
A couple of the Mullards and two or three of the RFTs flashed brightly when powered up. To the uninitiated, and even us old timers, this can be disconcerting to say the least. This is normal for European tubes of a certain vintage and is not a defect. It’s just that the filament flashes brightly for a second or two then settles down to its normal glow.
I’ll start with the tube I’m most familiar, simply because I had a quad of these close to hand when the TU-8340VK arrived.
Tung-Sol 12AT7W/6201 New production tubes made in Russia. The going rate is about 19 to 22 US dollars each. (~$27 to 31 CDN)
Sound: The sound of these tubes was balanced once broken in. That doesn’t mean much, not having compared them to any other tube – but the Tung-Sols didn’t offend, which is a good start. Bass seemed extended and reasonably articulate, mids were clear, and the highs struck a good balance between too dull or too bright. The sound of these tubes in the Elekit, optioned as described above, was very good even in comparison to a much more expensive amp.
Mullard CV4024 A 12AT7 equivalent that was made in the tens of thousands for UK military spares, probably to help keep the Mullard factory open. As such, they are some of the least expensive Mullard NOS tubes around. The manufacture date on these is 1985. Between 40 and 50 US dollars each is what they will set you back. (~$55 to 68 CDN) These particular tubes don’t have ‘Mullard’ printed on them, but the “R” code (see picture) indicates that they were made in the Mitcham UK factory. The same tube is available with the Mullard name and logo, but usually costs an extra 10 or 15 bucks.
Sound: Take what I’ve said about the Tung-Sols and add about 25%. Bass was as deep, but a bit more detailed and articulate, with slightly better control. Mids, whether vocal or instrumental, were just a bit more “there”, in that they seemed to reach out of the speakers and grab a bit more of the listeners attention, in a good way. Highs were a bit brighter, and that can be a double-edged sword, especially with overly bright speakers like the Triangles. With less bright speakers, the highs sounded just fine.
RFT ECC81 These are tubes of East German manufacture, from before the Berlin wall fell, so figure they were likely made prior to 1989. They can usually be found for between 18 and 20 US dollars each. (~$25 to 28 CDN)
Sound: These tubes sound like they’re channeling the sound of old Telefunken smoothies. That is, if you buy in to the stereotype – no pun untended, well maybe a small pun – that Telefunken smooth plate tubes were all about the midrange. The RFT’s put the emphasis on the midrange and lower treble. The bass isn’t as extended, nor does the high treble seem quite as articulate as the Mullard or Tung-Sol. Vocal sibilance is spotlit, which is not a good thing. All in all, these tubes don’t have the balance I’m looking for. They might work well in other applications, but in the Elekit they didn’t make the cut.
As Meatloaf said, “Two out of three ain’t bad.”
The Tung-Sol and Mullard are contenders. The RFT, not so much, for what I value in a listening experience. Is the Mullard worth approximately twice as much as a Tung-Sol? It depends how much you value that 25% more performance, and whether you think it will be even audible to you in your particular component and system.
I know what you’re thinking: “So how does this help me, my phono stage uses 12AX7’s and my line stage 12AU7’s?” I’m sorry, but I can’t give you a definitive answer. But one thing I’ve learned recently is that a lot of the new production tubes sound at least OK, and some of them darn good. Could Tung-Sol 12AU7’s and 12AX7’s at $22 and $17 US (~$31 and $24 CDN) each respectively be as good as the 12AT7’s tested here? Who’s to say, but the price isn’t crazy, and I’d take a chance on a pair.
Other new production tubes that might be worth a try are the Russian-made reissues of famous brand names from yesteryear, Mullard and Genalex for instance. I quite like the Genalex E88CC and KT77 tubes. Tubes from the Genalex 12A series could be worth a try, though they do run about $60 CDN each. (I’ve heard some of these, they’re excellent. -Ed.)
Here’s the thing about tube shootouts: equipment and listener preferences vary so much, that I can’t really predict which tube someone else might perceive as “best”. I can suggest ones to steer clear of and ones that might work well. This should narrow the field a bit, but in the end you just might have to try a few different ones to find your favourite. I try to avoid very expensive tubes in my shootouts because I don’t want nasty comments from disappointed tube-o-philes.
Is it worthwhile chasing down rare (read: really, really expensive) NOS tubes? Let me tell you a story. A few years ago I acquired a pair of Valvo Hamburg first generation NOS, NIB 12AX7 long plate tubes made in the 1950’s. When used in the first gain stage of my phono preamp they were not nearly as quiet, by a large margin, as the Sovtek tubes they replaced. Positioned further along the amplification chain the noise might not have been objectionable. If you are buying tubes for high gain positions – a phono stage for instance – it’s best to pay a little extra and have low noise ones selected. I didn’t pay much for the Valvos, but don’t ask if I’ll sell them, my cousin has his eye on them.
The Valvos made me think of the hundred-plus year old bottles of wine that are auctioned for lottery jackpot prices. The wine is not fit to drink; it long ago turned to vinegar. It’s just the collector value they’re being sought for. Decent quality new wine and reasonably priced new and not-so-old NOS tubes are readily available. Don’t pine for expensive old wine and tubes. Get a new bottle on your way home tonight and get some new tubes too. Pop the cork and spin some tunes. It’s a great time to be a music lover.
My Usual Rant
This is where I usually nag you folks about putting a few hours on new tubes as soon as you get them. I took my own advice, for once, and sure enough one of the NOS tubes expired after about five hours use. It had been purchased from a reputable vendor and was replaced without charge.