Tubes Asylum: REVIEW: CBS 7728 Tubes by Luminator Questions about tubes and gear that glows. FAQ

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I had thought that the CBS tubes I’ve been trying were from the 70s. So I wish to thank the others in Audio Asylum who corrected me, and pointed out that CBS was in the tube business from the mid 50s to early 60s. That makes these tubes older than a lot of us, certainly older than I am. So I am amazed that something which is 40 years old continues to push the boundaries of audio, even today, in 2001.

I first got into tubes in the mid-90s, when a friend of mine purchased a Sonic Frontiers SFL-1, which uses a single 12AT7. And now my AudioPrism Debut II/Red Rose Music Model Two uses four 12AT7s. In between, I have used 12AT7s in various VTL amps and in the Ear Max headphone amp. I witnessed my friend swapping tubes in the SFL-1, and he and I have continued our quest to find the best 12AT7s.

Until now, we have been frustrated. Most of the brands we have tried have that typical, warm, slow, murky, and rounded sonic signature. We want and need a 12AT7 which sounds fast, clean, detailed, and transparent. Well, I think we have a winner in the CBS 7728.

The CBS 7728 does not blur image outlines. If you have heard XLO’s and MIT’s top cables, you will know what I mean. Each instrument has its own identity, not meshing with other sounds. Images are not big, round, and diffuse. They are right there, tightly and clearly in focus. Because the CBS 7728 refuses to blur image outlines, transparency is well maintained. You can “see” between, around, and above the images.

The CBS 7728 does not reign in dynamics. This tube exercises good control over the movement of the music, whether from soft to loud, medium-loud to a little louder, or loud to SCREAMINGLY LOUD. If you find the CBS 7728 to be a little too stiff and controlled, go with the Sylvania Gold Brand 6201, which ebbs and flows with more liquidity. But in terms of speed, control, and intelligibility, the CBS 7728 runs all over the various Telefunkens and Mullards we have tried. With the CBS 7728 in place, you will be an active participant in the music, not just a listener. If the Mullard family is my toothless (and dead) grandpa, then the CBS 7728 is a great white shark in its prime.

With the CBS 7728 in my amp, death metal and thrash retain their bite. With other tubes in place, these types of music come off sounding like adult contemporary. Underneath the ugliness of Cannibal Corpse’s “Butchered At Birth” are some interesting guitar riffs and melodies. These are totally obscured with lesser tubes, which turn the whole album into sonic sludge. With the CBS 7728, you can hear exactly what goes on in the studio. You will be able to hear how Britney Spears’ tracks were put together. You will hear and appreciate the fact that Elvis, unlike Ms. Spears, sang his songs all the way through. But you know what? With the CBS 7728, even stiffs like us can dance like ‘N Sync! Is that the coolest or what? The CBS 7728 has enough resolution so that when you listen to Joe Satriani’s albums, you can hear how his newer Ibanez guitars have cleaner-sounding bridges.

The CBS 7728 does not artificially roll off the treble. The Police’s Stewart Copeland’s cymbals have their full attack, ring, and decay. Van Halen’s “When It’s Love” is different from your average rock song, in that Alex Van Halen hits his cymbals in tune with the chorus. The CBS 7728 keeps the vocals and cymbals separated from each other, yet, they are also in step rhythmically. And on the aforementioned Cannibal Corpse album, the cymbals actually have a ring to them. This natural ringing is completely lost when using dull-sounding tubes. On the other hand, I have heard some solid state preamplifiers and amps add some edge, crunch, and distortion to those cymbals. The CBS 7728 neither adds to nor subtracts from cymbals’ natural ringing. Consequently, my mind stops worrying about the sound, and is free to get off on the music.

Quite surprising for a tube, the CBS 7728’s bass is deep, detailed, and powerful. If you have been complaining that tubes just do not equal solid state in the bass, I urge you to listen to the CBS 7728. Savage Garden’s “Affirmation,” Sting’s “Brand New Day,” and any of Billy Joel’s albums from the mid-80s onward all have too much thick, fat, out-of-control bass. Other tubes are unkind to these recordings, the bass sounding as if Jabba The Hut just puked oatmeal all over the place. But with poor-quality recordings, the CBS 7728 does not lose what detail is there. Nor does it add any of that gratuitous bass boom or lower-midrange warmth. The CBS 7728 lets you know that the bass on Billy Joel’s “Innocent Man” is thick, constrained, and ill-defined, but it does not exacerbate the problem.

The Sylvania Gold Brand 6201 is in the same sonic vein as the CBS 7728, but it does not sound quite as razor-sharp, tightly-focused, and widely-extended. The SGB 6201 gives up a little control for some liquidity. Indeed, if you find the CBS too much of a good thing, you might like the more lyrical quality of the SGB 6201. Yet, the SGB 6201 still rocks hard.

If you hate this sound all together, hold your fire. Before you flame me, just relax. Simply chalk up these two tubes to the “I don’t like ‘em” category, and check out the Amperex E81CC made by Siemens, Telefunken ECC81 and ECC801S, and Mullard Gold Pin 6201. Those, I find, are the best of the warm and round category.

The CBS 7728 and SGB 6201 both are around $40 each. The problem with the CBS 7728 is that it simply is not available in any large quantities. And when you do find some genuine ones, a good percentage of those is noisy and/or microphonic. There is always hope that some long-lost stash will be found, but I am not holding my breath. The CBS 7728s that I have are giving me great joy. But if there aren’t any more to go around, then my joy will be short-lived and this review will have been academic.

-Lummy The Seahorse

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