distortion, discrete Class A front end and voltage amplifier of my own design, the single-ended output is DC-coupled into a pair of triodes (both enclosed in the 6SL7 bulb). These triodes are set up for maximum thermionic action which in tandem produces both the necessary drive and output biasing for a pair of complementary push-pull output current multipliers. Their output signals are then passively summed for the speaker output. The tubes are continuously operated at or near electron-emissive saturation which produces the pleasing, slightly non-linear tube overload characteristics ... required for the tube sound. The other condition ... is that the tubes must be interfaced directly with the speakers. Hence, the tubes receive a reflected and proportional DC load as they play into the output current multipliers. [The omitted parts refer to a famous research paper Mr. Butler references. It explores the reasons why tubes sound different from transistors and posits two specific requirements under which tubes come out ahead - Ed.]

• No output transformer
• Power amplifiers of any practical wattage level can be readily designed with this technology.
• No excessively high voltages. High quality lower-voltage-rated supporting components may generally be used (resistors, capacitors, diodes etc.)
• Drastic weight reduction. (Allows for 5 channels x 150w or more in a single chassis as in our 48 lb. TDB-5150 model)
• No maintenance. No periodic bias adjustments or re-tubing required. The amp may be left on continuously or switched via internal relay as desired by the customer.
• Low heat production. The thermionic tube auto biasing reduces operating and standby idling temperatures to about the same or lower than solid state amps of similar power ratings.
• All Tube sound: This proven new vacuum tube technology delivers as promised!"
  

For parts, there's "Sprague polypropylene capacitors, Vishay-Dale mil-spec 1% resistors; internal circuitry interconnections of the positive military-type screw connector style utilizing #10 hardware. A 700-watt toroidal power transformer. Exceptionally large heat exchange area on the internal heatsink as coupled into the large bulk and mass of the CNC custom chassis for remarkably cool operation." There's a blue-lit dimmer-controlled laser-cut logo as power indicator. There are silver circuit boards and Rhodium-plated silver contacts. Protection goes to the ends of the Yangtze river. It includes input fuse protection; thermistor protection against AC input line transient voltage spikes and surges; soft-start vacuum tube 5VDC warm-up for the 300B tube heater filament; 5 to 8 sec. turn-on and warm-up transient delay circuit that keeps speaker relay open until outputs have stabilized; DC offset monitoring circuit on the speaker outputs; short circuit protection; and an over-temp circuit breaker.



Back in spec land, there's a lowish input sensitivity of 1.4V for full 100-watt/8-ohm output. 47K input impedance. Dimensions of 17" W x 12.5" D x 10.5" H. 46 lbs weight. Worthy then of its very own short sentence so as to punctuate its distinctiveness is the power supply. It rates an absolutely gargantuan 2 Farad (2,000,000 or two million uF) to act as the immovable rock of Gibraltar. Battery-like, it is claimed to be essentially immune to powerline tweaks such as conditioners and fancy power cords. And then there's yet another giveaway to the Monad's unusual stature in the triode jungle. A claimed S/N ratio, A-weighted, of 105dB. Jimminy Cricket, that's CD or preamp territory and not even remotely close to -- never mind within -- the usual 'hood of no-feedback single-ended tube amps.


The ultimate amp? Does that header begin to seem sensibly relevant? On paper, the Monad appears to offer remarkable load invariance (the American Cabasse importer confided that the Monad is the only tube amp he's ever tried that could properly drive and control the big Cabasse models). It promises low-distortion SET sonics yet transistor muscle. It's got enough power to drive all but the most inefficient beastly speakers. Though offering in excess of 10 times its usual power, B.K.'s 300B will never need replacing. Unless you drop something on its purty head and break it. In fact, this 300B isn't "fully turned on" as we usually understand it. There's no B+ voltage applied but instead, some kind of reverse bias. Though how this hybrid/parallel implementation of valve/transistor devices in the output stage really works remains a mystery. Usual hybrids employ tubes in the front, transistors in the back. The Monad puts both tube and transistors in the back. Where the speaker sees and loads them. Without the usual output transformer.



That's another very distinctive trait of this single-ended tube amp. In fact, Butler calls such signal-path iron "hundreds of feet of phase-shifting, musicality-robbing wire and many pounds of induction-generating core iron to overcome". It's of course widely known that the quality of the output transformer is perhaps the greatest variable in valve amps. Nobody disputes that. Yet many would argue that it's precisely the presence of a -- superior -- output transformer that bestows on such tube amps their particular sonics. Certainly McIntosh and Audiopax would concur. After all, both firms use output transformers even for their transistor amps.


Whether demon or deva in the end, the Monad doesn't use an output transformer. That other toroid on deck isn't a transformer at all. It's an aesthetic balancing act hiding the massive capacitor bank. That doesn't rate the Monad a conventional OTL either. Unless a headphone amp, OTLs run endlessly paralleled tube banks to substitute for the speaker impedance matching usually handled by an output transformer. As a direct function thereof, nearly all OTLs run hot as sin. Think tube forest on fire. Not so the Monad. It's a high-power single-ended tube amp with neither transformer coupling nor typical OTL architecture. Instead, it uses B.K.'s "newly patented current-multiplying DC coupling circuitry that allows the 300B output driver tube to directly operate into a fixed ratio-reduced speaker output load. This novel design results in the production of authentic triode tube characteristics many times greater in power than the normal capability of 300B tubes yet retains all their superior musical qualities."

That's of course a deceptively simplistic explanation. It fails rather miserably at explaining why nobody chanced upon this solution a lot earlier. If it were really that simple. Butler's current patent rather suggests the opposite. Remember, most patents for tube audio applications predate the birth years of plenty of our readers. How many undiscovered ways to insert a tube in an audio circuit are there left? To see a 21st century patent awarded in this field is rare then. With neat categorizations eluding us like mad -- what to call the Monad, exactly -- it is some form of unconventional hybrid circuit. In one fell swoop, our nomad seems to eliminate what to many is plain wrong with conventional tube amps: excessive heat; excessive weight; power issues; load issues; distortion issues that arise from load issues; bass issues that arise from impedance and power issues; and pricing that's utterly inconsistent with measured performance and real power.



That latter point is of course fiercely debatable. Approaching twenty-thousand bills, the Monads are blatantly priced as über amps. Part of that cost surely ties to their near fanatical enclosures. Those are milled from 6" thick solid aluminum billet to eliminate any and all visible screw heads, provide mechanical integrity and "immunity from stray RF" and act as unified heat sinks. They purportedly require "hundreds of machine shop hours" to produce. If the Monads not only spec but perform as tube-based über amps, the pricing is in line with current dealer network convention. Though no less prohibitive. Prohibitive in fact is often the operative term when it comes to acquiring anything that's truly exclusive, hand-crafted and of superior quality. As such, each Monad is indeed hand-built by its inventor. Accordingly, it's in short supply. Best think of the Monads as custom creations. They just happen to be in production. They're not complete one-ups as the hot-rodded Cadillac for Billy Gibbons with Tube Driver Blue mobile amps above is.


Does this tie-in with car audio strike a shocked note of discord with your personal HighEnd-worthy überamp-bitions? It shouldn't. There perhaps is no better testing ground for a tube amp designer's real-world mettle than the bump & grind whereby imperfect road conditions and spirited driving rattle the dental fillings in tube amps. Save perhaps for the abuses musicians suffer upon their amplifiers on stage and on the road. Which B.K. has built for some twenty-odd years for quite the list of celebrity guitar wranglers as well. In my book, Butler's credentials then are exactly what you'd hope to see if no-nonsense engineering and reliability were to be in your thermionic future.