Tube Power Amp Reviews

There's also an argument to be made that the dynamic power of SETs is better than push-pull. I too cocked an eyebrow when I first heard this one, but Gordon explained: "In push-pull you've got the transformer's core magnetizing, collapsing the field, then magnetizing in the opposite phase, for one thing. And then the core of a single-ended amp has large amounts of DC current in it, and the inductance actually seems to create more power. In a sense, you not only have storage in the power supply, but also instantaneous power stores in the output transformer itself!"

And last, how close can you match any two tubes in a push-pull pair? Over time they drift, and one may drive more heavily than the other. Rankin: "When you lose the balance between the pair it creates distortion at the crossover point, which should be at zero. I believe that's most easily heard as a loss of microdynamics."

Tubecraft
Tube selection for minimalist-circuit single-ended triodes is more critical than in push-pull applications. The substitution of power tubes alters the sound in significant ways, as does swapping inputs. My favorite 300B (by a wide margin) was the beautifully crafted VAIC (pronounced vie-shh or vay-shh, depending on who you talk to) VV30B Type 1. These refined and elegant tubes are fabricated by hand in the old Tesla Research Labs in the Czech Republic. This model is a plug'n'play 300B equivalent. Rankin: "In regards to the 300B, the brown-base Golden Dragon 300B Super is the best value. If you have the extra money, the VAIC VV30B Type 1 is better sounding and will last a lot longer. In order after that is the Western Electric 300B, Golden Dragon 4300B, then the Cetron version." I bring you Gordon's tube musings because, as I experimented with different tube sets, I found him to be, not surprisingly, right on the money.

In fact, here's a cut'n'paste of an e-mail Gordon sent me regarding the tube complement:

"Jonathan: Here is a general overview of the tubes I sent you and why:

"The absolute best rectifier tube is the Mullard 5AR4, rebranded by almost everyone. No one made it better.

"The input tubes that I sent you are the Sylvania 6188, 5691 (black base) and the RCA 5691 (red base). The 6188 is a JAN 6SU7, which is basically the same as a 6SL7, but it's got more closely matched sections. I also find that these tubes have a lower plate resistance and a little lower gain than most popular 6SL7s or even the 5691. This tends to make the amplifier sound tighter and faster. It also has more air and extension.

"The 5691 was part of RCA's attempt to make a 'special' version of some of their tubes that exceeded the specifications. Out of this line were the 5690—a rectifier, very hard to find—and the 5691 and 5692 (6SN7 type). The 5691 is the only hot setup. The Sylvania version of the 5691 is better detailed and more exact in its reproduction compared to the RCA. Not many have heard the black-base versions because they were less sought after than the red-base tubes. The RCA sound is more midrangey and somewhat fat-sounding. I suggest it to customers who are searching for that old-time tube sound. To me the black-base are much better sounding and those will ship by default.

"Pricing update: The Cardinal XS with the VAIC VV30B Type 1 or the Western Electric 300B costs $7500. You can have them with the newly introduced VAIC VV30B, which is a less expensive version than the VV30B Type 1, for $7250. Or with the Golden Dragon 300B Supers for $7000. You can also choose between the 6188 or the Sylvania 5691 at no extra charge.—Gordon"

As Gordon suggested, the 6188 was significantly better-sounding in every way than the next-best black-base Sylvania 5691. The RCA 5691 red-base was sweet and a bit thick, and was my least favorite input—except during break-in, when its softer sound soothed the savage silver beast. Using the VAIC, the Sylvania 6188 (with one of the most fantastic tube accessories I've come across—more in a moment) and the Mullard 5AR4 rectifier allow for an increase from the Cardinal's regular 7.5W to 8W. The actual power will vary—up to 9W—depending on which input tube you use.

Wow. Nine watts!

Unhappily, one of the VAIC tubes expired mid-cadenza. Gordon shipped me a pair of Golden Dragon 300B Supers while he waited for replacements and a report. The Supers weren't bad—quite punchy and vivid, but not nearly as refined and graceful as the VAIC. Once I fitted the replacement VAIC tubes, I never took them out. This second set performed flawlessly. (I understand the factory has a metallurgist on the case. It's the ribbon filament that's causing the trouble.) In spite of these teething problems, I cannot imagine any single-ended setup that would not be much improved by the siren song of this lovely tube. All the best setups will have them. In the meantime, the newboy Western Electric 300Bs are warming in the wings, so we'll just have to see...

For the first 10 or 15 hours, the new set of VAIC VV30Bs sounded congealed and gritty, if in a single-ended sort of way, and lacked dynamics, air, and any sense of spatiality. After 20 hours, however, they showed their perfectionist origin and sounded forth glorious music. Let me bring you a few scribbles from my notebook to illustrate: "As I sit here listening to the fantastic new Opus 3 release, Music by Frank Zappa by the Omnibus Wind Ensemble (Hah!) (CD 19403), I realize there's a lot to be said for the brown-base Golden Dragon Supers. They're like GE 6550s in the Jadis JA 200s—not so pretty, less detailed, but more butch, punchy, and dynamic than the Sovteks."

Cablecraft, tweakery, & system considerations
Cabling these amps for best sound proved surprising. Goldstein and Markwell installed the Reference 3A Royal Master Control speakers knowing they'd partner the Cardinal XS amps for review. They set the speakers up with a bi-wire-ready pair of Siltech LS 4-240, and left us with various lengths of Siltech FTM-4 Gold for the front-end and a 4.5m length of FTM-4 Sg for the run to the amps. As mentioned, the amps are wired internally with both Siltech and Kimber silver wire, and the speakers themselves are laced through with the stuff. One could easily imagine that using Siltech throughout the system would make perfect sense.

But it was not to be. As the amps and speakers ran in, I became aware of a distinct and bothersome graininess in the treble. It seemed completely out of character; of all the qualities I'd heard ascribed to single-ended sound, graininess just wasn't one of them. I removed the longish run of FTM-4 Sg to the amps, and it became immediately apparent that this was the culprit. Not quite broken in? Perhaps, although the entire system had by this time more than 200 hours on it. Too much of a good thing? I'd like to think so. Even though Siltech wouldn't be our first choice for cabling our entire system, I'd have to say that they sound lovely and open indeed. (They'd pretty much have to at $2400 for a 1m pair of FTM-4 Gold, although Siltech makes a full range of cables including more modestly priced wire and accessories.)

Breaking my own principle of wiring up with only one interconnect family at a time, we found the perfect match for the preamp/amp connection with a length of Synergistic Research's Resolution Reference. It was...just perfect. I left Siltech throughout the rest of the system—including the speaker cables—which worked very well. Since I was mixing and matching anyway, I took the opportunity to change the front-end line-level interconnects as the mood struck. We had good results using Synergistic, XLO, Discovery Signature, and AudioTruth Diamond—all very pleasing. But the bulk of the review was done with the Siltech/Synergistic combo.

Electrical connections throughout the system were made by Michael Griffin's Essential Sound Products The Essence powercords, and Ted Denny's Synergistic AC Master Couplers. The Marigo Audio Labs RMX Reference B powercords were on the side for the moment, but I still consider all three to be at the top of the performance heap.

The Tweak Gallery was full. Three Shun Mook Mpingo discs on top of each speaker, left at 7 o'clock, right side pointed to 5. I also placed one Mpingo on the top cover of each amp in front of the rectifier tube, where there was some open real estate. The balance of the room treatments were as described in June's "A Matter of Taste" (Vol.18 No.6).

The amps were suspended on either Shun Mook Super Diamond Resonators or Michael Green Design AudioPoints, those relatively inexpensive all-brass "ballistic" cones that always manage to sound so consonant with music. All cables were suspended on Michael Green Cable Grounds. I did come to rely on that tube tweak I mentioned earlier for a significant boost in sound quality—they're MIDAS Tube Dampers from Bluenote SAS of Florence, Italy. I wrapped their springy coils around each input tube, and the result just wasn't subtle. I'm preparing an article on a couple of super tweak items, and this little brass and ebony affair will be described therein. It's a honey.

I also used Shakti Stones to excellent effect on the power transformers of the amps. Even their orientation atop the 'formers made a difference—as suggested by Gordon. More about the Shakti Stones (and the Bedini Ultra Clarifier) in the upcoming tweak article.

The CAT SL1 Signature was my primary reference preamplifier; I felt it a good match both sonically and price-wise with the $7500 Wavelength amps. Digital front-ends were the Forsell and Jadis transports and their matching D/A converters. (I have found over time that each DAC works best with its own transport.) Analog was traced by the reliable and superb-sounding Forsell Air Force One with either the Clearaudio Insider, Symphonic Line RG8, or a freshly tweaked vdH Grasshopper IV. ('Hopper update in the works.)

A matter of perspective, or you are here
The weeks passed as we burned in the amps and speakers and became more familiar with this system's sound. There's a lot of heavy-gauge Siltech hookup wire inside the Cardinal XS, and it all needed time to settle in and loosen up. We changed input tubes, swapped cables and footers, and tried different tweaks.

As we listened, I became aware of a certain readjustment that one has to make in listening to single-ended triodes. To really appreciate the glories of this technology, you must be open and flexible enough to alter your point of view and expectations. (A surprisingly easy task, given the quality of sound.) The presentation is entirely different. It's a bit like being with Kathleen's fraternal twin, Martine: in some ways so alike, in others polar opposites. (Thank goodness!)

The more pervasive push-pull technology is all about pinpoint focus and imaging, sharp edge definition, fast transients, tremendous apparent detail, and large, layered, airy acoustics, not to mention big bass. The trick is getting both the harmonics and tonal palette just so while doing these imaging tricks we've all come to expect from the best systems. Push-pull is simply great at re-creating the fifth bounce off the rear wall, or catching the inopportune flatulence of a nervous first violinist who wolfed his pastrami-on-rye at lunch. (Hold the pickles!)

Single-ended is a far different affair. Its charm and brilliance lies in a more close-up view of the origin of sound and its diffusion into the nearfield about the performer. You are aware of depth, layering, and overall recorded acoustic, but it's not as important as that moment in time when the original acoustic event occurs. Single-ended holds a sonic magnifying glass to this moment of creation, eschewing the larger picture for an enhanced view of its origin.

In fact, while I was pleased to note RH used his ears rather than the numbers when evaluating the Cary CAD-300SEI, I think he made a key mistake when he stated, of the Infinity Prelude, "...with its ability to be driven to satisfying levels using an 11W single-ended triode amplifier, the Prelude becomes the loudspeaker for such amplifiers." Well, RH, it's one way to go, but it's not the only way. It may satisfy some number of listeners, but many single-ended aficionados will insist upon listening full-range.

You see, I fervently believe in letting a thing be what it is rather than trying to make it something it is not. The point is, trying to get single-ended to "do" push-pull will surely disappoint. Single-ended does not do push-pull—and should not be asked to do so.