This summer I conducted an experiment that I hoped would answer a question that’s been on my mind ever since I heard that European Audio Team (EAT)’s KT88 Diamond vacuum tube would be made widely available in North America through their distributor, Vana Ltd., at the hefty price of $1795 USD for a factory-matched box of four (the KT88 Diamond is not available singly). Would it make sense to replace the eight output tubes in my pair of JE Audio VM60 monoblock amplifiers ($6400/pair when I reviewed them in 2013), whose stock tubes are already of decent quality, with an octet of third-party tubes costing $3590?

But time had presented me with an opportunity: Not long before, the VM60s’ stock KT88s, Genalex Gold Lions, had worn out, and I’d replaced them with a new batch of same from TheTubeStore.com for $59.95 each, or a total of $479.60 for four matched pairs. At the time, I wondered if I should try other tubes, but decided to stick with the Gold Lions -- I was very happy with what I was hearing from the VM60s. I hadn’t used the new tubes much, so they were still working at their best (they seem to last between 2000 and 3000 hours). The Genalexes are made in Russia; the EATs are made in the Czech Republic, where EAT makes all their products: turntables, phono stages, tonearms, cartridges, and 300B tubes.

A question of price

Comparing the sound qualities of tubes might seem odd. From what I can tell, the price of EAT’s KT88 Diamond makes it an outlier among tubes currently being produced (you can still find rare, new-old-stock for really high prices). As well as the KT88 Diamond, TheTubeStore.com sells nine other makes of KT88, from the Shuguang KT88-98 ($39.95 each) to the North Electric Graphite KT88 ($169.95 each), with most makes costing closer to $39.95, and all nine averaging $70.06 -- less than one-sixth the single-unit price of EAT’s KT88 Diamond ($448.75). How can EAT command so high a price?

I looked into the history of the KT88 Diamond. The first mention I found in the press was in 2004, which I assume is when EAT owner Jozefína Krahulcová first brought them to market. Her goal then, as now, was to make the best KT88 in existence by using construction techniques that are purportedly time-consuming and thus costly. Nor were her tubes cheap even then -- articles I read about them reported that four matched KT88 Diamonds sold for $1100 in the US and £599 in the UK. But while the high prices raised eyebrows, the tubes gained acclaim. On EAT’s website, I found a link to a review by outspoken audio critic Ken Kessler in the July 2005 issue of the UK magazine Hi-Fi News (Ken now writes our “SoundStage! UK” column): “It took, oh, all of two seconds to justify their existence, even in an amp costing a mere £999 -- or only £400 more than the set of valves on its own,” he wrote. Hi-Fi+ gave them a Product of the Year 04 Discovery award for 2004, reviewer Roy Gregory stating: “Once again, they seem expensive until you hear the results, at which point purchase becomes a no-brainer.”

As for the current price of $1795/four -- I guess a price increase in 15 years shouldn’t be unexpected, given inflation and all. I was also told by someone at Vana Ltd. that since 2004 EAT has steadily improved the tubes, so that could account for some of the increase.

Unrelated to price, I also learned that 2004 was when Heinz Lichtenegger, founder and owner of Pro-Ject Audio Systems, first met Jozefína Krahulcová, whose name is now Jozefína Lichtenegger. EAT and Pro-Ject remain separate corporate entities, however.

All in the listening

European Audio Team makes clever use of their acronym on the top of each box containing a quartet of KT88 Diamonds. Printed there is the company’s full name, as well as the slogan “Exceptional Audio Tubes” -- although, as I joked to a friend, EAT could just as easily stand for “Expensive Audio Tubes.” But is the KT88 Diamond “exceptional”?

At first glance, the KT88 Diamond’s looks don’t match its price -- different from my Genalex Gold Lions, but not better or worse, and certainly not at six times the price. There’s also no indication that the Diamonds will last longer than other KT88s, although EAT’s warranty of six months far exceeds the 30- and 90-day warranties of most other tubes I’ve seen. And it’s reassuring that the tubes of each quartet have been matched by hand -- you definitely want every tube of the same type that’s used in the same amp to be as close to the same spec as possible. Each box comes with a test report detailing the results for each of the four tubes -- something I’d never seen before. But the Diamonds won’t let your amp output more power than will other KT88s. For example, the VM60 is rated to produce 60W into 8 or 4 ohms, regardless of the make or model of KT88 used, and I have to think that will hold true for other amps. Mostly, it’s about the sound . . .

I keep a pair of Polk Audio’s RTi A1 speakers around to begin these types of experiments with. The RTi A1 cost $339.95/pair when Aron Garrecht reviewed it in 2010, but now costs less than $200/pair. They sound decent enough, but for me the Polks serve a higher purpose: They’re sacrificial lambs offered up to any new power amp I review -- or any new set of tubes for an amp. If something goes wrong when I first power up the amp, I’ll be happier if I blow up the cheap little Polks rather than the multi-thousand-buck speakers I mostly test. This caution goes back to the early 2000s and the arrival of a Perreaux amplifier. I hooked it up to a pair of speakers, and a little while later, a relay inside the Perreaux blew -- the amp then pumped out full power into one speaker, and fried its drivers’ voice-coils so badly that the diaphragms couldn’t budge a millimeter. Better safe than sorry.

Back to 2019. Up front in the system used for this review were an EMM Labs DA2 Reference DAC and Pre preamplifier, connected to each other and to the JE Audio VM60 monoblocks with Crystal Cable CrystalConnect Standard Diamond interconnects. Instead of feeding the EMM DA2 from a computer, I attached a Google Chromecast Audio wireless streamer to one of the DAC’s two TosLink inputs and streamed music from Tidal, using my Samsung S10 smartphone as a controller. Meitner Audio speaker cables connected the amps to the Polk RTi A1s. Power cords and distributors were from Shunyata Research.

I fired up the amps and all was fine. Then, beginning with Billie Eilish’s When We All Fall Asleep, Where Do We Go? (16-bit/44.1kHz FLAC, Darkroom/Interscope/Tidal) and continuing through many other albums, something unexpected happened: I listened through the Polks for several hours. That never happens, but this time there was something different about the sound. The Polks have always had a great-sounding midrange when driven by the JEA VM60s and their Genalex Gold Lion KT88s -- now that midrange was a good bit smoother, with more body and “bounce” to the lower midrange. Voices sounded even more captivating than usual, and music had a bit more drive. Overall, it seemed that the sound had taken a big step up in quality -- but it was too soon to know for sure.

I next hooked up the VM60s to a pair of Totem Acoustic’s Tribe Tower speakers ($5500/pair), which Philip Beaudette had just dropped off so that I could get them measured in the National Research Council’s anechoic chamber. (We’ll publish Philip’s review of the Tribe on this site in the next few months.) The VM60s with EAT KT88 Diamonds helped deliver a big sound from these speakers that really surprised me. Each two-way Tribe measures only 36.81”H x 7.01”W x 7.87”D, and has only three drivers: a 1.3” tweeter above two of Totem’s 4” Torrent midrange-woofers. Yet the bass reached down to a respectable 50Hz and maybe a bit lower, and they played pretty loud, even in my very large room (16’W x 18’L, opening behind into that much space again), which is really too big for them (given their size, they’re obviously designed for a smaller listening space). Add to that an almost alarmingly spacious soundstage -- sounds regularly appeared beyond the speakers’ outer boundaries -- and the Tribes sounded like speakers twice their size.

What stood out was, again, the reproduction of the lower to upper midrange, which was smooth and palpable -- the sounds had true body. I immediately noticed this with the outrageously catchy “Bad Guy,” from the Eilish album -- in fact, the propulsive sound of the bass and the focus on her voice made this a good test track for KT88s. The bass had good heft, and Eilish’s voice had smoothness and body, but not at the expense of detail -- I could hear into recordings every bit as well as, if not more than, I could with the Gold Lions in the amps.

That great bass and midrange were just as audible with Michael Bublé’s superb-sounding Bublé!, the nine-track soundtrack album (16/44.1 FLAC, Reprise/Tidal) of his NBC concert special of that title, aired March 20, 2019. Throughout, Bublé’s voice was intoxicatingly smooth yet ultrapresent, and the sound of his band had great weight. With this album, I also thought the VM60s’ highs were much cleaner with the EATs than with the Genalexes, as was obvious with cymbals -- they sounded more clean and airy. Finally, the soundstage seemed wider and deeper, which I think also had to do with the highs -- that increase of “air” around not only the cymbals but other instruments made everything seem . . . well, bigger.

At this point, I switched back to the Genalex Gold Lions to confirm the differences I’d heard. It was obvious that, in “Bad Guy,” Billie Eilish’s voice wasn’t quite as present and smooth through the Gold Lion KT88s as it was through EAT’s KT88 Diamonds. Also, the upper bass and lower midrange weren’t as fleshed out with the Gold Lions as with the Diamonds, and the Gold Lions lacked some drive in the bass -- there wasn’t nearly as much propulsion to the sound. The EATs might not have increased the VM60s’ power output, but they sure sounded more potent and forceful. That’s probably why, in his July 2005 HFN review of the KT88 Diamond, Ken Kessler wrote: “What we have here, my friends, is the valve equivalent of Viagra.”

The differences became much more obvious when I returned to Bublé! and a medley of three of the singer’s hits: “It’s a Beautiful Day/Haven’t Met You Yet/Home.” The clarity with the Gold Lions was decent, but with the KT88 Diamonds was markedly more so -- I could “see” more easily into the soundstage. Most noticeable, though, was the bass -- in comparison to how they sounded with the KT88 Diamonds, the Totems sounded almost anemic with the Gold Lions -- and Bublé’s voice was way less present, almost like the difference between FM and AM radio. The soundstage now was somewhat narrower and shallower. I then reinstalled the EAT tubes in the VM60s and played the Bublé medley again. Ten seconds was all it took me to come to a verdict: The sound with the EATs was fuller, more present, more alive, more detailed, more spacious. At this point, I realized that I was going to have a tough time boxing up the EAT tubes and sending them back to Vana. So I decided to prolong the pleasure and postpone the pain by running one more test, just to be really sure . . .

Because tube amps generally interact more with the speakers they’re driving than do solid-state amps (which typically has to do with tube amps’ generally higher output impedance), I wanted to try a third speaker: Monitor Audio’s Gold 100 ($2100/pair), which Diego Estan had just finished listening to and delivered to my house. He’d found the Gold 100s to sound very neutral, as do I. (Diego’s review will appear on this site in the next couple of months.)

I began with the KT88 Diamonds in the VM60s, then replaced them with the Gold Lions, then swapped them in and out several more times, listening again after each swap. The results were the same as with Totem’s Tribe Towers: regardless of the recording played, the Gold Lions didn’t have the same propulsion in the bass and midrange, certainly didn’t sound as smooth through the midrange, and produced a loss of cleanness and air in the highs. The sound with the Genalexes wasn’t bad -- it just wasn’t nearly as good as with the EATs. As Ken said, it’s easy to justify their existence.

Are they worth it?

Outwardly, EAT’s KT88 Diamond tube doesn’t look as if it should cost $448.75 (actually, $1795/four). Sonically, it’s a different story. Eight KT88 Diamonds considerably improved the sound of my JE Audio VM60 monoblocks. The JEAs didn’t become completely different-sounding amps, but they sure sounded better than before. What’s more, the level of improvement was far greater than any change of speaker cable, interconnect, or power cord I’ve ever tried. Still, was that improvement worth more than seven times the cost of my Gold Lions? In my opinion, it comes down to how in love you are with the sound of your tube amplification -- and if you have the money.

Be warned: If you fall down this rabbit hole, listen to the EAT KT88 Diamonds, like what you hear, but aren’t willing to pay the price, you might find yourself disappointed and frustrated -- once you’ve heard the difference, you can’t unhear it. That’s what’s happened to me. I’ve returned the KT88 Diamonds to Vana Ltd. But now that I know how much more my VM60s are capable of with these tubes, I desperately want them back.

. . . Doug Schneider
das@soundstagenetwork.com