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Reviewers: Marja Vanderloo & Henk Boot
Sources: CEC TL5100 CD transport with ultra clock; Audio Note DAC-2 Signature, modified, no digital filter
Preamp/integrated: TacT RCS 2.0 room control system; Audio Note Meishu, modified, with AVVT 300B, JJ, Tesla or AN 300B output tubes
Speakers: Avantgarde Acoustic Duo, internally wired with silver; Audio Note AN/Jsp, silver wired
Cables: Audio Note AN/Vx interconnects; Siltech Paris interconnects; Gizmo silver interconnect; Qunex 75 reference interconnect [in for review]; Crystal Cable CrystalConnect Reference interconnect, CrystalDigit S/PDIF RCA/RCA and RCA/BNC, CrystalSpeak Reference, CrystalPower Reference AC-Eur/IEC [on extended loan]; Gizmo silver LS cable
Power line conditioning: Omtec PowerControllers
Sundry accessories: IAR carbon CD damper; Denson CD demagnetizer; TacT RCS calibrated microphone and software; Exact Audio Copy software; Compaq server w/Windows Server 2003 and XP; Plextor PX-712UF [in for review], wood, brass and aluminum cones and pyramids; Rack of Silence & Discs of silence [in for review]; Gizmo's Harley Davidson cap; silver Buddha head
Review component pricing: $TBA - ca. $500 - $525/pr

KR300B: First Impressions
Tube gear has one disadvantage only. The sound changes over time, not suddenly but gradually and over an extended period. This provides our highly adaptive brain with a long enough period to constantly adjust to the drifting sonic emissions from our eventually sub-par glass bottles.

Causes of deterioration are related to the efficiency of your loudspeakers, the size of your listening room, its damping and the quality of the AC juice coming from the wall outlet. These are basically all environmental influences shaking, rattling and stressing the tubes. The next factor is you, the listener. Are you driving your little amp to the max? Do you listen for hours on end or for just 15-minute sound-byte stretches? How long do you take to warm up the equipment before listening? How much time do you let pass before performing a restart?

When deterioration of the tubes has been ongoing long enough, suddenly you do notice it. The sound gets dry and less lively. The naturalness you used to praise as highly as possible now becomes artificial and constrained. Bass starts to get loose; overall dynamics are down by several dBs. By this time, you're ready to admit there's a patient on your rack.

Sometimes during this stage, a dab of medicine in the form of a contact cleaner/enhancer to the pins can cause a little revivification but the chief damage has plainly been done. It's time for an investment - a sound investment.

If you are playing in the 300B league of SET worshippers, replacement tubes are abundant. They all are based on or inspired by the mother of all 300Bs, the 1930's Western Electric. Each and every brand adds its own flavor to the basic recipe. A little more current, a dash more on the dynamic envelop strength or a nice visual presentation with a glowing mesh grid. Sonically all brands sound different. It is up the customer to pick his or her favorite.

One of the possible choices is the new KR300B. This is not a 300B on steroids like the 24-watt 300BXLS of the same Czech make. The KR300B is a direct plug'n'play Western Electric-type 300B alternative. The plate runs at 300V and the grid at –58V - a regualr low power triode. So the electrical specifications are a match and all that matters now is sonic preferences.

When we received our review pair from Eunice Kron in Prague, the tubes went almost straight into the -- cleaned -- sockets of our Audio Note Meishu. After restoring power to the amplifier, the mains switch was flicked and the tubes got time to recover from their trip and settle in.

The first visual inspection of these tubes shows a very heavy-duty build quality. Where the WE 300B is remarkably lightweight, the thick glass of the KRs envelope adds noticeably to the overall weight. As we know from our visit to the KR factory, the glass used there is laboratory quality and the resultant envelope is capable of holding KR's signature high vacuum. The vacuum pumps at the Prague factory suck all air out of the tubes to reach a breathtaking 10-8 Tor rating. After activating the getter in the tube, virtually all causes of premature tube aging are eliminated. Neither part of the tube's intestines is prone to the slightest oxidation or worse, burning up.

After warming up of about half an hour, the first musical signal awoke the tubes. As a result, the air excited by the Avantgarde Duo loudspeakers reached our ears and the complex vibration to electrical impulse conversion in our inner ears ended up in abundant stimuli to the auditory cortex in our frontal lobes. In short, we heard music; rich
warm music with sufficient dynamics, a full bass foundation and slightly edgy highs. The so important vocal range frequencies was articulate and well defined. This was a preliminary listening session and after a few sample records, the system was set to a lower volume to allow the tubes to break in overnight and over the following day.

The second listening session was far more pleasant. The edginess had gone and the mids gained more air around them. Compared to other 300B tubes, the KR is not the one with the most bass though a satisfying quantity with enough dynamic punch is generated. In combination with the Meishu's output trannies, the highs roll off gently for the famous tube warmth. No harshness here. Cymbals are made of brass and reeds of reed. Transparency is the word that describes the complete impression best.

For a replacement of aging tubes or for new amplifiers, this KR 300B in the WE aisle is more than an excellent choice. Just don't expect to replace these tubes anywhere in the near future. KR's high vacuum tubes live a long life as we know from experience. With a given duty cycle of 20,000 hours and 2 hours listening per day, these tubes will offer 27 years of musical joy. We better get cracking then for a head start.

Incidentally, in our personal pantheon of 300Bs so far, we like the KRs best. They're followed by the VAIC now working under a different brand name [EAT I believe, at $400/ea., see right - Ed.] and then JJ, the latter being the cheapest. Some like the mesh-plate Sophias/FullMusic bottles. We think they are are a little lean-sounding but they do certainly look very sexy with their glowing innards. We tend to avoid mesh plates, however, and believe that a good solid plate does better based on what we've heard thus far.

Publisher's note: This tube is so new that final US retail pricing hasn't quite been established yet but Mr. Alfred Kayser, the US/Canadian/South American distributor for KR Audio, estimates a pair will come in between $500 and $525. A pair is enroute to Arroyo Seco for a 2nd opinion used in the Canary Audio CA-308 monos, as compared to Golden Aero and Aydn-branded bottles.
Manufacturer's website
US distributor's website