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The Lundahl Armada DHT SET Amplifier KIT

Dr. Harvey "Gizmo" Rosenberg
Guildmeister of the Triode Guild
Thermionic Techno-Shaman


I got an email from Dr. Snafu:

Dear Dr. Gizmo,

I read about the new Lundahl amplifier and was so impressed by its revolutionary potential that I decided to get involved…and demonstrate my power over all creativity. I think you should alert everyone that this kit will not be available until the end of November…around the time of your birthday.

Dr. Snafu.


I was watching a baby boy crawling, struggling to get up and walk. I was fascinated. Obviously no one was encouraging this tot, who was being constantly frustrated, falling down, over and over again…but he wouldn't give up. And then I heard the words that are so common in children…."No, no, let me do it myself", when they insist that they no longer want to be dependent and want to experience their own power. Then I thought about my twelve year old godson Lucas and the tens of thousands of times he has practiced his pitch.

Think about all the effort and energy we have expended, over our lives, to become master of some skill. How much effort do Americans spend every year on mastering sports, business, love, or spirituality? How many hours do Americans spend every year practicing their musical instrument? Think about the masters, gurus and guides available to teaches us how to master…. a golf putt, a tomato plant, …a guitar, … a trout, or race car.

Of course mythology, fairy tales and myths are filled with tales of the novice seeking the master to find truth…including Star Wars…and the wisdom imparted is always the same…what we are seeking is in our souls, and to liberate that power we must, in adversity, find faith, grace and courage…we must leap into our void. This is often times called an initiation ritual. This is the way, it has always been the way, and it will continue to be the path. And it is a taboo subject in our tribe, even though this wisdom directly applies to the audio arts.

Recently I have asserted that the reason our tribe's jargon has, over the last two decades, obsessed over "accuracy" is because its meta-context was so "inaccurate" relative to musical transcendence. Again this paradox is obvious, a taboo subject, and why there is such excitement in this current audio rebellion.

Here goes: The notion that we can shop our way into ultimate musical ecstasy is absurd, and is a completely inaccurate representation of the role of audio technology in the search for musical ecstasy. The dimension that has been almost completely ignored is our musical consciousness and the process that every human being, since the beginning of time, must pass through to achieve higher dimensions of experience. Full circle: Those who are looking for these higher dimensions seek out gurus, guides and master to liberate them from "the mind" that is holding us prisoner is a small space. This is the old audio mind of the last two decades. I am suggesting that the master is in you, awaiting for you to wake him.

Because I am our tribes Master Debater, let me get to my closing and winning argument right now: The Japanese have got it right, and we are learning very quickly from them. Pause: Yoshi Segoshi, importer of 47 Labs electronics told me this story upon his return from a recent trip to Japan…He met a artists who builds custom tube amplifiers for his clients, and only he will only work on them when his spirit is just right, because he knows his spirit is being transferred to the amplifier, and the quality of his soul determines the quality of their sound. At the concrescence of any art is a big neon sign that is blinking: THIS SPORT IS ALL ABOUT EXPANDING OUR AWARENESS.

Which brings me the question of..HOW TO or "How Can I expand my experience of music in my home", or "How do I get to the top of mountain, when there are no elevators, or stores"?

All that I can do is suggest a first step on this path. This is the path I have traveled and I traveled it because I followed those who went before me. This is the path Japanese audiomaniacs follow. Am I on a crusade? Yes, and I will encourage you to take this first step by showing you a glorious field of gold waiting for you if you jump into the void. Let me put this another way…I am going to tell you about an audio gizmo that is, in its class, the concrescence of coolosity, but you have to, just like in the myths, pass an initiation test to experience it. Think of this amplifier as the Excalibur sword stuck in the stone, and you wont be able to pull it out, unless you purify your heart by building your first SET kit, and I don't care which one it is and let your chat rooms guide you in your decision.


Rather than watch Bay Watch Japanese men hustle down to their local audio club and attend weekly classes in tube amplifier circuitry. Japanese men treat their tube circuits the way we Americans treat our custom made hotrods…if you want ultimate performance you must create it. Can you buy a Formula One car in a dealer's showroom?

While still ignored by wide segments of the high end audio tribe the stark simplicity of directly heated triode single-ended amplifiers ( a divine paradox from the 1930s) has stimulated a new wave of DIYers who are building their own amplifiers. Most American men are terrified of using their hands, don't know how to solder (which is just a little bit more difficult than brushing teeth) and are terrified of high voltage.

That is the "normal" mind that is keeping you out of music heaven. Don't be afraid of the high voltage in tube amps. In the process of learning how to work with high voltage you will get a shock, and it is okay…like getting knocked down when playing football…it is part of the game, Mr. Tough. Any twelve year old girl can build a single-ended amplifier kit. It is easier to master, and less dangerous than sex. It is easier to master than skiing and much less dangerous. It is easier to master than riding a motorcycle and is much safer. It is easier to master than golf and is much safer.

But the most important thing about building an audio kit is that it can completely alter your relationship to music, because it will, if you let it, completely alter your attitudes towards the audio arts. That is what initiations do for a living…like enlisting in the Army. A dimension of your awareness that was not available to you before, will open. Once you have discovered that you have the natural skills, then you will, with your new confidence take a few steps down the path, where you will meet the Guildmeister of The Triode Guild, and I will ask you to sit down, light up a fine cigar, sip some brandy, while I will tell you a true story that will inflame your imagination…and you will know…for the first time…that there is no limit to your musical expansion.

Let me say that another way: I want you to build your first amplifier kit, so you will be ready to build the first kit that the Guildmeister has designed… with a team of beaudacious triode bros' from around the world….coolosity has its ferocity. Trust me and yourself. Take the first step.


Don't be frightened and don't call 911. The trembling in your hand is not a sign of a stroke, or a brain tumor. You are feeling my excitement endowed in these pages, and you too are about to tremble. The reason these pages are trembling at 4.1 on the Richter scale is because the single-ended amplifier I am about to describe an aural matrix which is as different from "normal" single ended amps, as single-ended are from push/pull amps. The big deal is that Lundahl Armada is able to create a new DHT aural matrix.

This advanced circuit concept existed in the 1920s, and that is why it is one of those joyous artistic paradoxes that make the audio arts so exciting. This new DHT aural now exists because of "the team love" of three righteous thermionic dudes: myself, Jim Dowdy and Per Lundahl. Can you think of anything more thrilling then creating and experiencing a new form of musical beauty? Keep on reading and trembling because to explore the edge of art we must have the courage to go to that place where we are most vulnerable.

As a French tickler, here is a preview of this …..Armada: This SET amplifier kit is a gaggle of firsts:

  1. It uses only DHT tubes from input to output…made possible by the new AVVT 20
  2. Has two completely independent tube rectified and choke filtered power supplies: one for the front end and a different one for the output stage
  3. Employs le plus ultra "magnetic" coupling and loading: grid chokes, plates chokes, and interstage transformers
  4. The only tube which is constant is the first stage/voltage amplifier, which is the new mesh plate AVVT 20 DHT that is bigger than a 300B. The driver stage/second stage gives you the ability to choose different brands of 2A3 or PX 25 tubes. With your choice of any brand of 300B output tube means you have a staggering number of choices in "tuning", which is then multiplied by the number of choices you have in rectifier tubes.
  5. You can choose the impedance of the OPT that you prefer, 2.5K, 3.5K, or 5K. As you know mine is 5K, while most prefer 3.5K
  6. You can choose between fixed and variable bias of the driver and output tube…each sounds different.
  7. You can choose different operating voltages for the output tube from 350 to 500 volts
  8. You will be able to retrofit the output stage so that you can use some of the new super higher powered DHTs…without having to buy a new amp.

This level of amplifier "tuning" control has never been available to the music lover before. In effect our team is creating, not one amplifier, but one amplifier which is many…no, let me say that more accurately…YOU HAVE HUNDREDS OF DIFFERENT POSSIBLE CHOICES…you will never get aural boredom. That is the real benefit of 4th Wave Modality and is therefore the worlds first existentially accurate thermionic device.

But what is truly thrilling about this monument to directly heated triode beaudacity is that this 6-12 watt amplifier has got a very simple signal path but, the chassis is huge…almost the size of Texas, because each chassis holds TEN transformer and/or chokes, three directly heated triodes (audio circuit) and three rectifier tubes.

This is a very big heavy amplifier…perhaps the most awesome single-ended amplifier available either manufactured or as kit. Let us not forget this important truth of coolosity: carbon based male humanoid bi-peds have a primal need for very large and heavy toys…like cars, tanks, and big amplifiers. Let me assure you that this is the biggest and heaviest single-ended amplifier available. Like the 250 pound four foot tall Futterman OTL-1, this amplifiers says…"Your the dude". Yet, the circuit is so simple that your pet German Shepherd, Fritz, can build it. And if that is a slight exaggeration, then let me share this cunning: the purpose of the Lundahl Amada is to offer everyone who has built one of the increasingly popular simple SET DHT kits, a quick step to the top of Mt. SET. Or, for those who are not into DIY, I strongly suggest you buy the kit and have your local TV repairman build it for you.


Girls, can we talk honestly? This project is all about creating a fabulously cool audio gizmos that redefines the genre. This is the amplifier for the music lover who can no longer tolerate aesthetic subservience to an audio designer. Why do you assume that an audio designers has more refined musical judgment than you? This amplifier is able to speak, and it says" Only you know, the mysteries of your journey and I am here to bend and sway to its rhythms". You will soon discover why this is the last single-ended amplifier you will need to buy.

This amplifier will take ten years to review because that is how long it will take to experience all its different variations , and that is a good thing.


The DHT single-ended virus continues to grow because our musical consciousness has always been a more formidable force than the dysfunctional orthodoxy, known as audio "noise" engineering, that has dominated the audio arts for the last thirty years. In spite of DHT-SETs significant limitation in power and their very eccentric interaction with speakers, what they do right is so righteously beautiful, that what they do wrong seems insignificant. As more and more music lover's confidence grows they are trusting their ears more, and what they are hearing, in spite of the fact that most of these amplifiers are not of optimal design and are used with non-optimal speakers, is so "relatively" juicy that they join the movement. There is something quite magical about the DHT SET aural matrix, and it is completely different than the pentode push/pull and OTL aural matrix….and this project extend that unique aural matrix.

Remember I am talking about a circuit concept and their unique tubes that first appeared almost 90 years ago, at the dawn of audio history, reached their first golden glory at the end of the 1930s, disappeared and then re-emerged in America about seven years ago….because we needed more, so we chose LESS IS MORE. I love this paradox so much I eat bagels in the shape of 300Bs every morning.

Great advances in output transformer design, innovations in directly heated triode design by KR and AVVT, and most importantly your restless creativity encouraged, by the Internet, has fueled the expansion of this unique amplifier aesthetic. We must not diminish the influence of the emerging DIY market, made possible by the ease of building these starkly simple SET circuits. I remind you that even the most complex SET circuit is far simpler than a Dynaco 70. That is the good news.

The sad news is that in spite of their popularity, few who own these amplifiers have got a clue to how good they sound because there are, still literally, no proper speakers available for them…or any other tube amplifier for that matter. I assure you based on my recent conversation with both speaker and driver manufacturers that, in spite of the ease in making higher impedance speakers, there is a reluctance to do the right thing because they think you don't care or you are too stupid to know better. You can change this with email.


And now on to thermionic existentialism: 4th Wave Modality. The notion that there is an existential hypothesis at the foundation of the audio arts will probably make most audio designers belch, fart, scratch their butt, or have brain brown out. Yet, this is obviously is true because at the edge of every art is self-reflection, a potential of opening to deeper dimension of awareness; a piercing through the mediocrity of normality to a higher plane of "non-normal" sensual awareness. I call this ecstasy. You call it getting down with your bad funky self..or whatever.

Obviously, every human being is an instrument who must be tuned for optimal perception, which is why our pre-linguistic invention, music, is such a perfect reflection of that truth. This is such a fundamental truth that I have asserted that "non-tunable" audio systems, are anti-musical, though they are, at the moment, universal. Fidgeting with cables, spikes, and various other tuning devices, from this 4th Wave Modality point of view are attempts to correct a fundamental flaw inherent even in the most expensive audio systems.

Spend $125,000 on a Bosendorfer piano and how many hours must be spent in tuning it, and then how many times do you retune it as you and your instrument become a wholey ecstatic musical unit? Did you believe that musical awareness is static? It isn't and never is, because our musical consciousness is constantly evolving. So it is with our audio system, and for the Guildmeister of Triode Guild, the definition of a state of the art audio system is one that permits us, to constantly retune it as our tune becomes more refined.

Those with the intellectual right stuff, consider this: While it is accepted as being "normal" for us to have complete control of our phono systems, by changing tone arms or cartridges, it is also considered "normal" that we have absolutely no control over our amplifier's aural matrix.

Consider this question carefully: Where is the distinction between instrument and musician? The proper answer is…they are a wholey one and inseparable and that is true for you and your music system, and again, this is the existential imperative of tuning, because your musical tune is an ever-changing tide of ecstasy.

Am I biased when I assert this existential expansion is only possible with tube circuits? Of course, because only they are inherently tunable, and my 4th Wave Modality campaign is just the next step in evolving thermionic consciousness, and all that we are doing is to extending tubes nascent advantage…and more.

The more is to stimulate in America the development a community of audio artisans and companies, similar to the one that exists in Japan: craftsmen who are ready to build, for the confident and sophisticated music lover, custom made tube amplifiers. This is the perfect business for the Internet. In literally every other form of male pursuit from fishing, to clothing to cars to golf, it is accepted that if we are searching for the ultimate coolosity we have no choice; we must go the custom made route or we must get on the DIY path. There is an enormous potential here for existing tube gear manufacturers, who inherently work on a very small scale to begin a custom manufacturing division.

As the father of the modern OTL I was the first to preach the evil of "transformer iron" in my 1984 book, Understanding Tube Electronics, so why have I become a champion of iron rich circuits? I remind you that I was to first, in these pages, to praise Nobu Shishido's interstage transformer coupling in WAVAC amplifiers, and again in this magazine, the first to yodel the praise of Sun Audio's transformer phase splitter push/pull amplifier The more intensely I appreciate OTLs the more I can appreciate the unique aural matrix of iron rich DHTs. How much do I appreciate this new aural matrix polarity?….just give this piece a chance.


DOT 1: As I was reviewing the Sun Audio amplifier the American Zen Audio Master Lynn Olson (Oregon) turned me on to Lundahl transformers which he was using in his own new push/pull 300B design, asserting that the Lundahl iron was of the highest quality. Last year I surfed to the Lundahl web site and immediately contacted Per Lundahl, and order some iron. After being very impressed I started a dialog with Per, and convinced him to go radical….let's create a "showcase" amplifier for Lundahl iron…that would be a colossus of coolosity. Per got down on the idea of shredding the edge of DHT beaudacity. Full speed ahead.

DOT 2: Jac Van deWalle (Germany) who is sales manager of Alessa Vaic's new company AVVT also suggested that I explore plate chokes. AVVT (Czechoslovakia) had just released the AVVT 20, the first DHT tube that has suitable as a voltage gain tube for tube amplifiers, meaning it wasn't microphonic like the 45, or 10Y. I also surfed to Jim de Kort web site (Holland) to check out all of his experiments with magnetic coupling and loading of DHTs.

DOT 3: I have one of those big thick Japanese books (Tokyo) that is an encyclopedia of tube amplifier designs and schematics that goes all the way back to the 1920s ( RCA amps made in New Jersey in 1926 were my favorite) and I was noticing that the some of the first tube amplifiers looked just like the newest trend in Japan…iron rich DHT SETs

DOT 4: I was e-mailed by Jim Dowdy (North Carolina) who had surfed the Triode Guild web site and we started to compare triode coolosity and he insisted that I explore plate chokes and interstage transformers. Jim had a vast collection of different brands of iron. (Italy, Japan, Canada, America). Jim fanned the fires which were smoldering.

DOT 5: I remember seeing in the Italian audio magazine Cositirure (Rome) a very interesting SET design that employed all DHTs. The author claimed that for ultimate tonal glory the entire tube chain had to be all DHT…no indirectly heated triodes.

DOT6: Nobu Shishido (Tokyo) suggested that to get maximum beauty from a DHT it takes (literally) an amplifier to drive the grid of the output tube.

DOT 7: Be simple: I have been preaching the value of the simplicity of SET circuits which preserve the natural tonal wholosity of music. This also implies that feedback, which can improve bass and lower "normal" distortion, also discombobulates the midrange and causes all sorts of "non-normal" distortion. I love bass, especially the large mouth variety on a summer day in Georgia, but refuse to sacrifice the midrange juice for it.

DOT 8: Be Very Stiff: This is very hard for flaccid tube amplifier designers to grasp. The best is tube regulation, second best is real good choke filtration. This is the oldest and best wisdom, so why is it so ignored in America.?

D0T 9: An amplifier is a modulated power supply: This means that the sound quality of your power supply is as important as the modulator, which means we must pay attention to quality of rectification.

DOT 10: Only you know what sounds best to you. Why shouldn't those of you who are ready take responsibility for your aural destiny be the conductor of your symphony. The notion that I, or any other audio designer has a higher sense of beauty than you is both insulting, and denies the fundamental reality of all amplifiers: they are tunable, if designed properly.


As you know my senses are extremely sensitive (bat ears/hound dog nose/snake tongue), and every time I received an email or spoke to Jim on the phone I could detect the aroma of barbecuing pork loin, but I knew this was the thermionic fires burning in Jim's loins, and I loved it. I loved it because I love men who are passionate about musical beauty and who are committed to pushing and exploring their own frontier. This is man at his most beaudacious best. Jim inspired me with his "iron connoisseurship". We started to ship each other different tubes and transformers from our collection and compare experiences. This is what I love about the Hawg community…the feeling of brotherhood is palpable, and it has the subtle spiritual power of a good Havana Cigar and small batch Tennessee sipping whiskey.

As you know in November of 1999 I too started to experiment with plate chokes and interstage transformers and it took a long time, about 30 minutes, to convince me that this was the path to get maximum juice from DHT SETS, and Jim inspired this leap into the iron void.

How impressed was I? Impressed enough to press Jim into this project because I want to concretize my belief that, you, the gifted amateur, like Jim, like Nobu, is where we find the real dynamo of this audio revolution. Or let me say this another way: It appears to me that because of the Internet there has been a shift of creativity to the gifted amateur, and Jim is a shining example of this new dynamic force.

Let me describe this team effort in terms of a classic male dream modality, by using the analogy of men's most popular subject on the Internet. Okay?

Think of the entire directly heated triode revolution as one of those women who appear on web sites like "Live, Young, Sex Craved". Now stare at her body as she wiggles and squirms……she now has your attention…just like directly heated triodes. Think of those fun, easy to build and inexpensive SET kits as her elbows and knees. Think of the more expensive SET kits as her breasts. Now if I asked you to pick one tiny part of her entire body to concentrate on, what would you pick? Just think of the Lundahl Armada as that special place (your favorite place) that can totally dominate your imagination…after the first time you experience it. Do you understand this analogy, or was I too intellectual? Are you ready to dwell in your place of ultimate sensual pleasure?

Can you imagine our team's excitement over the possibility that we may have created the only competitive audio gizmo to the one gizmo that makes all intelligent grown men act like junk yard dogs? I hope everyone who reviews this amplifier or builds it, holds it to this high standard; a standard that no other amplifier has dared aspire to.

It was also very helpful that Jim had experience with almost all of the other transformer brands, and had done enough experimentation on his own that it took Jumping Jack Flash to agree on a circuit concept…..Be Very Simple, Be Very Stiff, and Be Tunable…nothing new…just Hi-IQ. The circuit we are using is one that Jim has been tweaking and refining for a very long time.


When Per Lundahl, the current President of Lundahl Transformers was a tot, his father , who is now 70 and retired, taught him to play with transformers. Sitting on his father's knee by the fire in the living room Per was told marvelous tales about knights in shinning armor, directly heated triodes, damsels in distress, pentodes, evil sorcerers, plates chokes, goblins, and how the mystery of magnetic occurred.

I have asserted that what is so cool about audio iron is that even though, for example, two OPTs, or plate chokes, have almost identical electrical specifications they will sound very different…and for good reasons. When we deal with audio iron there is an essential dimension of mystery that arises out of many design factors including the mechanical design, and that is why my coolosity meter pegs in the red when I grock Lundahl transformers. Nothing in the world looks like them, and I love them. They have the bold naked mechanical beauty of a power house, or turbine. The Lundahl transformer dynasty is completely unique in this regard…they only manufacture open frame designs because they believe that this is the way for maximum performance…


Let's put on our time transportation hat and travel back to my father's living room in 1926 where he is listening to the radio while his father and mother are reading the newspaper. We notice that under the table is a big battery which supplies the DC voltage for the radio, and once a week a man in a truck comes and replaces it. Did you know that Guy R. Fountain, the founder of Tannoy loudspeakers, started business as a "battery charger". In the good old days there was no AC rectification so every home that had a radio had a battery and because battery charging was expensive the goal was to save every last milliamp of current.

When we look at the schematics of amplifiers from the days of battery power we are looking at a world that only had directly heated triode tubes, and a normal amplifier configuration was an input transformer connected to the grid of DHT, which used an interstage transformer as coupling to a DHT which was connected to a single-ended OPT. Golly Miss Molly how is possible that these primal circuits resemble so closely today's edge of the art? The answer is, the closer we are to the time paradox, the closer we are to the edge.

As you know a tube won't do any work unless it is "loaded" and then it has to be "coupled" either to another tube, audio device or speaker. This loading and coupling can be accomplished with resistors, capacitors (a combination of both), another tube, a transistor or with a choke or transformer. When you use a choke or a transformer, I will for the sake of this article call this "magnetic. There are many theories about what is the best way to load a tube for maximum linearity relative to gain.

The electrical nature of magnetic loading and coupling is very different than all other methods and it translates into a vast sound difference relative to other forms of loading. During the good old days of battery power, plate chokes rather than plate resistors were used as a way of loading a tube because this saved current. When you are using a battery why waste current being dissipated through a high value resistor? And in a world that had not yet mastered the art of small, high voltage capacitors, magnetic coupling, i.e. interstage transformers made sense.

I am not implying that the chokes and transformers that were available during my father's childhood are of the quality that we have available today, but…my favorite SET DHT amplifier; the one I am listening to in my living room right now…from a circuit point of view, looks like one right out of his 1926 living room.


Those who have fallen madly in love with the unique sound quality of magnetic coupling all reflect Nobu Shishido's words…" I don't know why it sounds so good, I just trust my ears". Lynn Olson has speculated that when a music signal passes through such a magnetic field it is just like the music ingesting LSD". Lynn's technical insight must be right because there is a very dramatic difference in the sound quality between this technique and all others, and this is the simplest, the most expensive, and to my ears the most beaudacious.

On the other hand there is a small group of thermionic savants who are claiming that those high value plate load resistors are a serious aural contaminant, and explains why so many have chosen constant current sources as loads created with either tubes or FETs. In my NYAL preamps and in some of the TUBE GOD input circuits I used FETs as loads for the tubes.

Let me compare value here. Let us assume you are using one of those ultra cool plate load or grid resistors and you paid $2 for it, though a "normal" resistor could cost twenty cents. I am suggesting that by substituting a choke in its place, which may cost between $75 and $150 you will be catapulted to a much higher and unique dimension of musical beauty.

I know of no other amplifier that exploits "magnetics" in the way that this Lundahl Armada does. The combination of "magnetic loading" of the grid and the plate of the first gain stage which is a DHT is also completely unique made possible by the new mesh plate AVVT 20.

The other righteous intuitive element of the Armada is the second stage, drive circuit, which you are right to assume looks like a 2A3 SET amplifier. That is exactly right because to make a great drivers stage it takes a great amplifier, one that can deliver the voltage and current through its interstage transformer to make the grid of the output tube sing. The difference between the sound of typical 6SN7 as a voltage amplifier and driver stage and the Armada's equivalent circuitry is the feature that separates this amplifier from all DHT SET normality.

PAUSE: I remind you of my comments in my Sun Audio review: A great amplifier needs a great driver stage, and most American amplifiers do not have driver stages that are powerful enough. My criticism of those multi-tube push pull amps that use a single miniature dual triode as a driver should now make sense, because in this amplifier we are using a 2A3 as a driver for just one tube, a 300B.


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