Tube Power Amp Reviews

I've never written a love story before, but then, there's always a first time. This romance concerns the stunningly anthropomorphic Jadis Eurythmie II (mostly) horn speakers and the petite, jewel-like and vivacious Jadis SE300B amps—a 10W single-ended triode design with paralleled output tubes.

Kathleen and I, having flung ourselves into single-ended's embrace, have become, to some fashion, quite experienced. I've described the purity of presentation available with the Wavelength Audio Cardinal XS monoblocks when coupled with the Swiss-made Reference 3A Royal Master Controls in these pages (January '96). Using the Eurythmie speakers, which supplanted the 3As in our system, we've listened to Gordon Rankin's Wavelength Cardinal XS monos, the Kondo-san Audio Note Kasai parallel 300B stereo amplifier (next SE review to come), the ebullient and eager-to-please Cary 301SE 300B stereo unit, and the Jadis single-ended triodes, as well as our reference Jadis JA200s (yes, Jadis also does push-pull).

And we evaluated a cornucopia of 300B tubes which were slipped into the waiting sockets of these amps: the VAIC VV30B and the less-costly VV300B; the long-anticipated and very suave Western Electric 300B (see my interview with Westrex's Charles Whitener elsewhere in this issue); Chinese Golden Dragon 300B Supers; the not-quite-ready-for-prime-time ESTi 4300BLX; Audio Note-branded 300Bs (carbon-plate ESTi, I'm told). (For the hoopy-scoopy on these tubes, see my "Brace of Bs" sidebar). At this point, even Jimi Hendrix would consider us experienced—if not quite in a Purple Haze. Most of the time.

The Jadis SE300B: the Long View
This amplifier is drop-dead gorgeous. Working front to back on the elegant nonmagnetic highly polished stainless-steel chassis, you'll find an On/Off switch on the front apron with a green LED signaling "power on." There's no provision for warmup/standby mode as with Jadis's larger amps. Topside, there's an oozing-with-casual-quality power transformer, somewhat more diminutive in size than the lump of a hand-wound thing that crouches darkly on the chassis of the JA200s. That's followed by a pair of 5R4 rectifier tubes, a pair of caps, and the elegant Jadis signature square black potted output transformer with its elegant gold top-plate. Behind are "ignited" the two 300Bs, and a single 6SN7 at center chassis rear, flanked by another pair of caps. On the rear apron, there's an IEC power cord socket, an input RCA jack, and a single pair of binding posts.

Jadis SE300B: the Technical View
I'll quote from a spec sheet on the Jadis parallel single-ended triode amplifiers prepared by Jean-Paul Caffi. I haven't paraphrased his words very much, as I found the charm and humor inherent in his Technical Franglais to be without peer in communicating the concepts behind them.

"The SE300B supplies a power of 10W RMS and functions in pure class-A with single-ended mounting (the two tubes are in parallel) with an automatic bias [(footnote 1)]. The two high voltages, driver and power, have vacuum-tube power supplies. The bandwidth (at –3dB) is from 20Hz to 20kHz, without any feedback. The driver stage, powered at 400V, is built around a double-triode 6SN7. The two elements of the tube are mounted in cascade. The output stage is powered at 320V, which allows the tubes to work in the best conditions. The filament voltage is very finely regulated. Like other Jadis units, the output transformers are handcrafted without any gap in the magnetic circuits, and are used well below their full possibilities (they can be employed on 250W amplifiers.) It is important to have a large output transformer because a direct current crosses the primary in this construction, while in a push-pull construction, the direct current in the transformer primary cancels itself out."

I couldn't have said it myself, isn't it so? And before I cancel myself out, how about let's getting to the sound!

Tube matters
The Jadis amplifiers were delivered with a quartet of matched ESTi 4300BLX tubes (evidently from the same Chinese factory that churns out the Golden Dragon BLX.) In addition, there were a quartet of JAN 5R4WGY rectifier tubes from Chatham Electronics, made in the ol' U.S. of A. (These were egg-cup style 5R4s, with a large solid base that extended up part of the way around the glass envelope.) JAN stands for Joint Army Navy, by the way. In addition, there were two input 6SN7s not marked for origin or brand name.

A surprise package arrived soon after from what must be the nicest guy in audio, Wavelength's Gordon Rankin. "I thought I'd send you input and rectifier tubes that'll work well in the Jadis," he explained. Now I smell teen spirit! A public merci, Gordon. (As J-P Caffi seemed quite willing for me to try other tubes in his amps, I felt it very apropos to do so.) Gordon had sent a pair of his favored Sylvania 6SN7s, along with Tung-Sols, NOS (New Old Stock) red-base GEs, Golden Dragon 6SN7GTs, and very unusual looking 6SN7GTYs from the British Valve Electronic Company, whose glass-bottle interiors were coated in black.

I tried all the input tubes with some interesting results. Gordon pointed out to me that the relationship between the input tube, the capacitors used in a particular design, and the output tube affects the sound in significant ways. Keep that in mind—the following description reveals the sound of these tubes in the Jadis' circuit.

As I have always found with Golden Dragons of whatever type, they were exciting, dynamic, but slightly bleached and white-sounding throughout the frequency range. They proved fatiguing over the long haul—just too thin in the end. The Tung-Sols were a pleasant taste o' Olde Tyme Tube Sound, much lushfullness, not terribly transparent, and not very dynamic or extended. The Sylvanias, which I expected from Gordon's experience to sound the best, didn't. They were indeed wide-band and vivid, extended, clear, and spatial, and did great bass, but they proved a shade uninvolving and "hi-fi" like. They sounded a little too clean—music seemed robbed of its emotional content.

The input tube that really floated my boat was the NOS GEs. "Yup, these are the ones!" exclaimed an excited Ben Lichtenstein, an audio-crazy of our acquaintance who had come over to listen to the system. He can hear—the GEs had just the right combination of extension, tremendous air, transparency, rich harmonic structure, and tonal color. In a word, magic. Interestingly, Gordon mentioned that the Sylvanias work much better than NOS GEs with Hovland caps, so once again, be aware that everything in-circuit can make a difference. Relax, open your ears, and have a ball.

As for the output tubes...ahhh, therein lies a tale. The ESTi 4300s went south of the border almost immediately. One pair fell way out of balance, one tube nearly burning itself up while the other sat practically dormant, its filament barely lit. Same with the other matched pair, but here the dominant tube was gassy (sputtering blue light in the bottle) and began sending spitchy high-frequency bursts through the Eurythmies. Out, out, damned spot!

I got on the horn (!) to Frank Garbie, who quickly supplied two matched pairs of brown-base Golden Dragon 300B Supers, which some feel are a better bargain than GD's more expensive black-base 4300BLXs. These worked just fine, sounding enjoyably dynamic, bold, and vivid. They created a large soundstage; had good timing, rhythmic pace, and great bass; and sounded fast. They stayed in the amplifiers until the Absolutely Fabulous Western Electric 300Bs showed up. These Ever-Suave (apologies to ManleyClan™) 300Bs became the reference output tubes for the review. (See my sidebar on 300Bs for details, and check out my interview with Western's Charles Whitener elsewhere in this issue.) As it transpired, importer Garbie has made arrangements with Western Electric, and their wonderful 300Bs will be standard kit on the Jadis SE300B. Truly, a match made in heaven.

And what of the VAIC tubes? In a somewhat comical twist of audio fate, the VAIC tubes simply wouldn't fit into the Jadis amps. The tube sockets are slightly recessed, held in place by a short pair of bolts that terminate with a nut on the top chassis. The VAIC tube's glass envelope becomes very wide almost immediately above its base, and these securing nuts interfered with their seating completely. Pretty funny, if you ask me. Victor Goldstein, VAIC's importer, was somewhat crestfallen. Ex-Goldstein associate and current Jadis importer Garbie was ecstatic!

Goertz cable
We tried many different speaker cables with these little beauties, and eventually settled upon one that was perfect matched in every way—the Alpha-Core Goertz MI Ag silver ribbon cables. In conjunction with XLO throughout the rest of the system, these cables sounded above all ultra-clean and delightfully fast. You'd think a flat ribbon would be an invitation to the RFI Heebie-Jeebies, but this was absolutely not the case. Quiet, full-bodied, apparent DC-to-light extension, extreme high resolution, wonderful spatial qualities, these cables let the Jadis amplifiers be all they might. No editorializing whatsoever, aside from a certain lightness to the deep bass than could be corrected with the crossover adjustment.

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Footnote 1: We're talking self-bias here, with a resistor, rather than an auto-bias circuit that requires a negative supply.