Can you live with only a few watts of amplifier power if they're really great watts? Don't answer too quickly.

The race for bigger and more powerful audio amplifiers seemed to coincide with the Detroit horsepower race, and perhaps the two quests for ever bigger power were related. At one time 25 watts was enough for a "muscle amp." Today ten times that scarcely qualifies.
     There was a reason to make amplifiers so big. Designers had found a way to make speakers tiny, but at the price of efficiency. A full range speaker could fit on a small bookshelf, but it needed 200 watts to play louder than a whisper. Still, the transistor made high power available at low cost.
     The pendulum has swung the other way, as you've no doubt noticed. Many a modern speaker boasts of high sensitivity, and such speakers are being matched with new amplifiers that are large and expensive, but are--by established standards--flea-powered.
     This is one of them.
     The new low-power fashion made possible an operating mode that had been abandoned decades before: single-ended operation: using just one tube or transistor block at the output instead of a complementary push-pull pair (see the Why Single-Ended? sidebar on the page opposite). No huge claims for power are made (the KR brochure claims 20 watts, though other company literature suggests 18 or 25 watts--we'll return to this shortly). None of these figures will draw attention from the engineers of the Pink Floyd concert tour. Nor from anyone who thinks too much power is like too much money in the bank.
     The brochure already mentioned shows an address in Lugano, Switzerland, but in fact the amplifier is Czech. Dr. Riccardo Kron, a tube fan from years back, got together with former engineers from Tesla to develop a new version of the popular Western Electric 300B tube. The 300BSX is similar enough to the older tube that it can actually be used in amplifiers using the 300B, but it has a higher current rating, resulting in a maximum power output of...well, we'll get to that shortly.
     The KR 18 is the lowest-priced of the KR models, and the only one with controls on the front panel. We had planned to review it in UHF No. 56, but the box of tubes, which should have contained four pieces, turned out to contain more like 74 pieces. What's more, a repair came to more than just popping in a new 300BSX tube. KR recommends resetting bias (not really a user adjustment) after a tube change. We finally got a new amplifier, with tubes intact this time.
     We broke it in with the Gershman X-1 and SW-1 speakers, simply because they also needed some hours run up on their clock. Though the KR is made for speakers far more efficient than the Gershmans, it sounded astonishingly sweet and smooth during the few dozen hours of the run. We noticed something else too: if this maneuver had been done in winter, instead of in the midst of the hottest summer in living memory, we could have switched off the furnace!
     Even in the largest system the KR won't pass unnoticed, but it is rather more attractive than most hardware. The rather ugly black tube cage shown on company brochures has been replaced by individual chromed tube covers that give the KR a look that is at once futuristic and retro.
     Because the tubes and their covers dominate, you scarcely notice the somewhat spartan front panel, with its two metal knobs (volume and input selector) and its power indicator. The power switch? It's on the rear, and a long reach too, a clear indication of Kron's opinion that you should never turn the amplifier off--just buy a bigger air conditioner.
     There are four pairs of inputs, plus an output marked "mon" (for "monitor"), which can feed a tape deck, though there is in fact no tape loop. The jacks are possibly a little cheaper-looking than you'd expect in this high-rent district, though we liked the well-machined output posts, which feel like something J.A. Michell would turn out. If you use bananas, be sure the posts are tight, though. There are four pairs of posts... presumably for biwiring, because driving a second pair of speakers with this amp borders on hubris.
     Conscious of the need to run this amplifier with efficient speakers, we ran the tests in our Omega system, feeding it into our Reference 3a Suprema II speakers, with their 91 dB efficiency rating. However we made a mistake, and as we shall see that made the amplifier sound disappointing at first...

Would you like to read the full text, with illustrations, of the review of theKR 18 BSI amplifier? Click here to order the print edition of UHF No. 57.