Brilliant Corners

In 1976, a Soviet fighter pilot named Viktor Belenko made an emergency landing in Hokkaido, Japan. He was flying a MiG-25 supersonic interceptor jet and, upon touching down, requested political asylum. This proved to be a stroke of brilliant luck for the Americans. The MiG-25 remains one of the fastest and highest-flying aircraft ever produced, and Belenko's defection allowed them to have a tantalizing look at the technology inside.

After the US Air Force took the plane apart piece by piece, the Japanese returned it to the Soviets in 30 containers, charging them $40,000 for crating services. Later, the Soviets sent the Japanese a $10 million bill for missing parts. Both invoices are still outstanding. In the meantime, Belenko became a US citizen through an act of Congress and, after changing his surname to Schmidt and marrying a music teacher from North Dakota, settled in the Midwest and co-wrote a book about his ordeal. He died at age 76 in Rosebud, Illinois, this past September.

Among the top-secret loot found inside the Soviet jet was a large, heavy triode vacuum tube used as a regulator in the power supply of the MiG's radio. It was known as the 6C33C. (The enormous electromagnetic pulse caused by a nuclear explosion would fry a transistor. Tubes were used in military equipment with such an eventuality in mind.) As it happens, the 6C33C also offers unusual and promising abilities in less dire applications: remarkably high transconductance and current-handling ability combined with very low impedance. This triode can create some serious watts without requiring a heroically large or complex output transformer. In the 1970s and '80s, the Soviet military complex produced the tube in vast numbers, so new-old-stock examples are still widely available. Perhaps not surprisingly, the audio manufacturers best known for working with this device—Balanced Audio Technology (BAT) and Lamm Industries—are American companies founded by Soviet immigrants.

BAT VK-80i integrated amplifier
My introduction to this fascinating triode, with which I share a birthplace and approximate date of issue, was the BAT VK-80i integrated amplifier ($12,000; footnote 1). Visually, the amplifier does bring to mind the MiG and, more broadly, the Cold War aesthetic: With its fierce incised metalwork, large footprint, and LCD display on the front panel, the VK-80i looks decidedly martial. If you told me that the VK-80i's function was to measure the outflow of heavy water from the control rods of a nuclear reactor, I might believe you. Then again, I majored in poetry at a liberal-arts college, so deceiving me about technology doesn't require mastermind-level cunning.

The fully balanced, push-pull VK-80i produces a nontrivial 55 triode watts per channel from two pairs of output tubes operating in class-AB while relying on a very restrained 3dB of global negative feedback. Four 6SN7 tubes perform input duties. BAT co-founder and chief engineer Victor Khomenko (those are his initials in BAT's product names) told me that the amp can push out significantly more wattage than that. Conveniently, the BAT uses an autobias scheme that compensates for fluctuating line voltage and aging tubes. It also does away with internal fuses, relying instead on a protection circuit that monitors each output tube's behavior, muting the affected channel in case of malfunction.

On a recent morning, I spoke to Khomenko via Zoom. We quickly switched into our mother tongue, which I think was fun for both of us. I left the Soviet Union when I was 9 and wholly ignorant of consumer electronics, and during our confab I learned the Russian terms for things like "amplification stage" and "idling current." Thanks, Victor!

Khomenko grew up in Leningrad (present-day St. Petersburg), where he built his first reel-to-reel tape recorder at age 10 and went on to work in consumer electronics. (He's still obsessed with reel-to-reels—he sent me a photo of his listening room (above), which appears to house a forest of these machines along with a pair of Avantgarde Acoustic Trio horn speakers.) In 1979, Khomenko immigrated to the US and found himself, somewhat unexpectedly, in Wilmington, Delaware. He had $400 to his name. (My family and I arrived the following year in the somewhat more spacious environs of New York City.) He soon joined Hewlett Packard, working in gas chromatography, and had a hand in the design of the steroid testing equipment that led to Canadian sprinter Ben Johnson's disqualification at the 1988 Olympics. But his love of music—mostly classical, followed by jazz—and audio kept needling at his soul until, in 1993, he formed Balanced Audio Technology with HP colleague Steve Bednarski.

While working on the design of the first BAT power amp, the VK-60, Khomenko considered the usual beam tetrodes like the KT88 and the 6550, but decided they weren't sufficiently linear. He also ruled out large radio transmitter triodes like the 845 and 211 because of the lethal voltages and massive transformers they required. The 6C33C solved both of these problems but introduced one of its own: The tube has an unusually wide range of sample-to-sample variation and a high failure rate. According to Khomenko, during the selection process he discards a great many 6C33C-Bs. He strongly suggests that customers source replacement output tubes directly from BAT.

Khomenko is an empiricist at heart and relies heavily on computer modeling to design his gear, but he told me that the VK-80i measures no better than "pretty well." To finalize the design of their products, he and Bednarski use their ears. In a 1995 interview in this magazine, Khomenko said this to contributor Robert Deutsch: "Although measurement is very important for designers, the usual measurements in typical reviews are not as meaningful for the average consumer. I think magazines like Stereophile should be reducing the number of measurements, not increasing them. For the average person, it's very difficult, even impossible, to predict sound quality on the basis of measurements."

My time with the VK-80i began with a bit of waiting. Initially, the left channel muted after a few minutes of play, and Bednarski quickly diagnosed a faulty output tube. After I replaced the left pair of 6C33C-Bs, the amp operated with nary a hiccup.

I connected my sources to one of the BAT's three single-ended inputs using Auditorium 23 interconnects, and the BAT to AC using AudioQuest's Thunder power cable and Niagara 3000 power conditioner. I took advantage of the VK-80i's high impedance (6–8 ohm) speaker outputs and 18' runs of AudioQuest ThunderBird ZERO speaker cables to connect it to the Klipsch La Scala loudspeakers.

Let's listen: I've recently discovered Pretaluz, a 1998 record by Angolan singer Waldemar Bastos (Luaka Bop 6 80899 0029-1-2). Produced by downtown New York guitarist-singer Arto Lindsay, it features Bastos's languid tenor, which takes on a remarkable range of tone color, and a small band of Angolan and Portuguese musicians. Stylistically, the music mines a kaleidoscope of influences: Afro-pop, samba, fado, morna, as well as traditional Angolan music-and-dance forms such as semba, rebita, and kizomba. The recording, which Luaka Bop issued on vinyl for the first time in 2023, sounds vivid and rich.

Listening to the LP's opening track, "Sfrimento," I was struck by the vigor, scale, and dimensionality the BAT brought to this record. Bastos's voice issued from within a cavernous soundstage, about 10' above the La Scalas, and when the background voices came in, they were positioned well behind it. The music sounded effortless, well sorted, and perfectly controlled: Even when the arrangement got busy, I was able to easily discern and follow every element. And the sometimes startling dynamics of Bastos's singing were conveyed with beauty and bracing force and without a hint of strain, breakup, or distortion.

The VK-80i shares this majestic presentation with the Line Magnetic LM-845IA, another large-triode powerhouse, but sounds less obviously "tubey." In fact, at no point during my time with the BAT could I hear any emphases, omissions, or other deviations from a flat frequency response: It's quite possibly the most neutral-sounding tube amp I've heard. But unlike some amps that create a sense of neutrality and control at the expense of vitality and color, the VK-80i allowed the recording to sound alive, saturated, and liquid.

I'd be remiss not to mention the BAT's knack for transparency, aided by its very low noisefloor. Listening to Rachel Podger play the Suite No.3 in C Major, BVW 1009 from J.S. Bach Cello Suites on violin (24/192 FLAC, Channel Classics/Qobuz), I was treated to an explicit, exciting depiction of her faster-than-usual tempi and dancelike approach to pieces that, in less capable hands, can be stolid and even plodding. But the BAT also revealed how the odd decision to record Podger in a hugely reverberant recital hall obscured some of the filigree of her playing and made her sound frustratingly distant.

Further kudos to BAT for the VK-80i's stellar volume control, a 90-step resistive ladder that changes loudness in 1dB increments; the volume and active input are displayed on the front panel. Also terrific is the hefty, all-metal remote, which, in addition to the usual functions, can dim or turn off that bright blue readout. Though I haven't tested it, I'm confident it can also tenderize a veal cutlet or, with enough arm speed, disable an intruder.

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Footnote 1: Balanced Audio Technology, 1300 First State Blvd. Suite A, Wilmington, DE 19804. Email: steve@balancedaudio.net. Tel: (302) 999-8855. Web: https://balancedaudio.net/.