PENTODE PUSH /PULL
AMERICA'S MOST CRITICAL CRITIC
RETURNS TO HIS ROOTS and CREATES
A NEW THERMIONIC AURAL MATRIX
TO SAVE THE SOUL OF ROCK AND ROLL
HOW $45 WORTH OF PARTS AND A
TWENTY FIVE YEAR OLD IDEA
CAN GIVE YOU AN AURAL WOODY
REMINDER: In the 21st century 99.9% of Americans are still living in aural poverty, and are clueless. According to the Digital Devil, Rock and Roll music is: 5% about the music, and 95% about grinding adolescent pelvises, marketing formulas, hype costumes, fireworks, MTV, concerts that are exciting rituals, but sound that is so turdacious we must wear ear sickness bags.
If you are into the low IQ path of audio hype, bail now, because I am going to take you deep into pentodosity because it is the only way you will understand how to optimize the potential of this rock and roll music messianic modality.
This will be a daring adventure because it will be the first time you will be treated as an intelligent adult..relative to pentode amplifiers. Note: I am not now discussing small signal pentodes, which is a very different animal.
As you know no one has been more critical of this amplifier modality, and much of my aggravation is based on, what I consider the "wrong turn towards wretched excess" that American audio designers promoted for this modality, my experience with OTLs, single-ended, and my boundary shredding designs from the 1970s.
How did I know it was time to return to deep pentodosity?
THE BEARDED BURNING "BRITNEY" BUSH
SPEAKS TO ME ONCE AGAIN
The last time the burning bush spoke to me was in 1980, and told me to go and find Julius Futterman, I was deep into pentode push/pull amplifiers, which you can view on the Triode Guild web site. In February 2001, I was walking in Central Park, with my bullet proof vest on, and once again, saw smoke and fire spurting from a bush, and as I approached it there before me a mystical apparition appeared, that looked like Britney Spears with angel's wings, wearing an MTV T-Shirt and Wholey Mystical Cow..she had a beard and was holding a 6550 in one hand, and an EL 34, in the other, and she was pushing and pulling with her pelvis in that special MTV way. When I looked closer I noticed that Britney was no longer an eighteen year old virgin nymphomaniac, but was about thirty years old and much pudgier and wiser looking and then "poof" the smoke, and the burning bush, and Britney disappeared.
DEEP PENTODE PORNOGRAPHY?
I love men's love of pornography because here we have men paying a great attention to the smallest possible nano-details. What is so fascinating about looking at the same old, same old, time and after time? The answer is.the tiny details are different and matter and so it is with pentode push/pull, and it is my job to take you on a journey into the tiny details of pentode amplifiers so you can view them with the same pleasureful intensity that you view your favorite pornography, or hot rod magazine, or fishing catalog.
We are going to review every little squiggly wiggley, and create a new vision of rock and roll beauty that will definitely pass your most stringent Woody Test.
WARNING: DON'T LET APPEARANCES FOOL YOU
They are big, they have lots of tubes in them. They are the glam boys of audio magazines covers. Their circuit boards are crowded with expensive looking parts. They generate enough heat to cause global warming, and they cost more than an average American car. They are loved and adored by American audio reviewers, and rich white guys, who need expensive toys. But don't confuse sound quality with size. Trust the me on this I have created some of the biggest amplifiers in the cosmos, so I know the impulse.
PAUSE: A few years ago when I was making lots of presentations on Wall
Street I bought four FAUX Rolex watches for $20 each. At a distance it was hard to tell these watches from the $20K gold Rolex Oyster Perpetuals worn by men to announce their success. I did some creative gizmology by taking these watches apart and reassembling them so I had two faux watches on one band. Then I wore one on each wrist, so it was obvious, when I talked that I was wearing $80K worth of watches, which impressed all the men in the room who were wearing just on $20K watch. This should prove to you that I know how intense men's needs are for owning "power totems".
FORWARD: Unfortunately, the same logic does not apply to amplifiers the opposite logic applies, and these big powerful pentode push/pull amplifiers, which are inherently unreliable, are now like the dinosaurs which became extinct due to the Internet. Their death has made room for the evolution of a newer, more relevant form of pentode amplifier life form and it is going to be the savior of rock and roll.
Do you get my focus? Not rich white guys who can't dance, but,you and me and all of the other horny music men in the cosmos who deserve a better rock and roll diet.
HOW HIGH DO YOU WANT TO GET?
How vain can I be? Check out the NYAL OTL-1, Triodzilla and my 4th Wave Modality Amplifiers..and then once again, check out my pentode push/pull amps from the 1970s. In all honestly, I think I am forced to create these concrescent works of tube art because I like the view from the heights, because I am so short. I want to help you discover your high point, even if you are tall. Are you ready to get really serious about pentode amplifiers, because if you are you are going to have to change your mind?:
Start thinking in terms of the optimal pentode aural matrix, not big metal boxes with lots of tubes that can produce high horsepower driving speakers that are all wrong for tube amplifiers. Let's see if you can make a connection between elements of an amplifier, its input, phase splitter, tubes, and all of its other design elements and the aural matrix you are creating.
The Hi-IQ path is to accept the artistic/aural limitations of pentode tubes, so we can exploit them, so we can reach new heights of aural refinement by thinking outside the "normal" design box. Conventional thinking yields conventional results, and in America that means substandard musical pleasure. Do you have the courage and confidence to pull the flush lever on the bogus?
Stop wondering which is "the best" amplifier, and start thinking of "systems" that express your unique view of aural ecstasy. This will be possible because with your advanced understanding of pentode amplifiers, and by participating in the Triode Guild chat rooms you will become a "Rockmeister".
If you are looking for perfection, neutrality, or accuracy, stop reading now and surf to the Martha Stewart web site.
The reality is that though billions of music human hours are spent listening to rock and roll, rock and rollers don't have a clue about the thrill of rock and roll, because they are in an aural prison, though they believe they are in music heaven. Have I stumbled on an ancient myth? Yes, and the only way that rock and rollers are ever going to get out of their aural jail is with pentode push/pull amplifiers not OTL amplifiers, and not single-ended amplifiers and not the pentode push/pull amplifiers that are made for rich white guys who love wretched excess.
Am I crazy believing that a pentode tube amp can be made sophisticated and affordable and will rock the rafters?
Or, to put this is the in right demographic jargon: every year millions of rock and rollers are growing up, and a small percentage (hundreds of thousands) will get tired of the taste of Texas Road Kill and will be discover the taste of barbecued sirloin tubes, and never go back.
I have now explained why I am taking on the daunting challenge of changing your mind, and the minds of millions of rock and rollers about pentode push/pull amplifiers, because realistically pentode push/pull is the best amplifier modality for those who have escaped the "MTV sound jail". I consider this challenge more daunting than convincing the Soviet Union to celebrate Christmas with America and more important. The youth of America deserves better music diet: 99.9% of rock and roll tastes like Texas road kill in August and this is harming the health of American youth. Maturing rock and rollers must also have a healthier aural diet .because WE ARE WHAT WE EAT .AND LISTEN TO.
SHORT TRIP BACK IN TIME TO
REVIEW THE TERRITORY
Pentodes power tubes were first created in the 1930s because they were superior to directly heated triodes in many electrical characteristics they were more efficient., meaning they could disipate more current, and their internal construction, meaning their extra electrical/mechanical elements; their screens, improved the flow of electrons within the tube, reducing a certain kind of distortion, but at a big price because everything has a price.
You must remember that the major impulse in the audio arts, for its first one hundred years was efficiency, not refinement, and any output tube that could produce more power, at lower "normal" distortion figures was considered a major advancement and it was. But the price paid, and this subject is just now being re-investigated is that these tubes are NOT linear, and must have lots of feedback to correct their non-linearity. This puts is a major limitation on their ability to create an optimal aural matrix BECAUSE TIME COHERENCE is a big deal if you are searching for ultimate magic, and feedback destroys time coherence.
Why is feedback an essential feature of pentode amplifiers. Answer: (1) feedback is used to correct for their basic non-linear character, and (2) pentodes have very high plate resistance, almost three times the plate resistance of directly heated triodes, and feedback is needed to get the output impedance of the output stage sufficiently low to interact properly with loudspeakers. To get a little deeper a 6550 has a plate resistance of almost 35K, but these tubes are usually used with 5K output transformers. This is not an optimal tube/output transformer relationship but "normal" and taboo.
(NOTE: The reason that triode connected pentodes are so desirable, under certain circumstances because in the triode mode these pentode's plate impedance is usually reduced by two thirds and they become more linear)
By the early 1940s pentodes were becoming the norm in home audio, especially because the smaller pentode output tubes worked so well. A small pentode tube could produce more power than a much larger directly heated triode, that was much more expensive.
The consumer electronics revolution after WW II was based on the pentode output tube, with names like Fischer, Marantz, Mc Intosh, Dynaco, Harmon Kardon creating a new "hi-fi" industry exploiting the 6L6, EL34, KT88, 6550, and their kin. The "EL84" became the mainstay of the increasingly popular integrated receiver.
And let us never forget that the "pentode sound" is the sound of the electric guitar
Along come transistor audio and you know what happens. What happens is a an audio counter develops based on the pentode push/pull amplifier which gains a cult following because any gifted listener can tell that these amplifiers sound much better than the "new and improved" zero distortion sand based amps. Yet, even these "new wave" pentode amplifiers, were not very sophisticated, because the "new tube audio companies" that were manufacturing them, entered the " horsepower' race against transistor amps, rather than take the higher and more refined path. Enter Dr. Gizmo in the mid-1970s.
I was a pentode tube amplifier maniac buying..tweaking, experimenting, and my conclusions are now well known there is a continuum of push/pull pentode beaudacity from power to refinement, and you have to decide where you want to be on that continuum, and anyone who tells you that you can have ultimate refinement and ultimate power, deserves a second circumcision.
THE PURSUIT OF SWEET SLAM
An Appropriate Gizmological Response In 1970s To The Newly
Emerging Sex, Drugs And Rock And Roll Aesthetic
Looking back, with the benefit of twenty five years hindsight, the design decisions I made, made sense, and are now the foundation of my new push to take push/pull much higher.
FULL CIRCLE PARADOX: You will discover that my experiments with push/pull pentode amplifier was the basis for developing the Futterman OTL-1, and now, once again, this pioneering work is being reapplied to pentodes.
Our goal is not to make a pentode push/pull amplifier sound like an OTL, or directly heated triode push/pull, because that would be like trying to make a banana taste like an apple. There is no way, all things being equal (and they never are) that a pentode amplifier can have the refined sweet aural matrix of a directly heated triode amplifier. And there is no way that a directly heated triode amplifier can have the power and slam of pentode amplifier. Adults have to make choices.
Our challenge is to take what pentode push/pull amplifiers do better than any other type of amplifier and extend their ecstatic aural matrix, and to do that I must narrow my focus, and get very deep into a new tube amplifier aesthetic one that I pioneered in the 1970s well to be honest I didn't really pioneer it I just took an old idea and used it in a unique way.
In my previous writings I have asserted that pentode amplifiers were, for most musicmaniacs, the key to experiencing, for the first time, the deep musical mystery of rock and roll. My goal is to wean rock and rollers away from their turgid transistor based aural mediocrity. To do that I must create pentode amplifiers that have a new level of slam and sweetness, and affordability that heretofore has not existed in this modality of amplifiers before SO YOU CAN EXPERIENCE ROCK AND ROLL MUSIC IN A HIGHER ECSTATIC MODE.
STOP: Do you get my drift Mr. Hi-IQ sailor?. Want more refinement? Move over to directly heated triode amps, but you will sacrifice some of that pelvis pumping Britney Spear juice that rock and roll and MTV is all about, at a price you can afford. With directly heated triode amps you need speakers that have higher efficiency too.
FORWARD: What do I mean about taking slam higher? What I am really talking about is the weakness in most "normal" American pentode push/pull amplifier's power supply design. This is a taboo subject in America for some weird reason, but FACT: an amplifier's power supply is in series with music output, and determines ultimate aural matrix quality. It might be helpful to think of your amplifier's power supply as its engine. What good is a beautiful body (the audio circuitry) when hidden under the hood is lawnmower engine?
If you want to experience the outer dimension of rock and roll you need a Dodge Viper V-10 motor with a supercharger and nitrous bottle, and Dr. Gizmo's goal is to develop this level of performance and I apologize for taking the pomp out of my circumstances, but the way to achieve that is over twenty five years old and I stumbled on it first..and then exploited this notion in the OTL-1.
Now let's get to the nitty gritty of rock and roll's juice: The foundation of rock and roll is what is happening below 400 Hz and that is where all tube amplifiers are having a problem because their power supply is being drained of energy when heavy bass energy is produced, which causes the bass line of the music to sound very soft and flabby. The reason so many prefer the bass response of solid state amplifiers is because they can deliver the slam at the lower frequencies that make rockers twitch.
Twenty five years ago when sex, drugs and rock and roll reigned supreme I was compelled to discover if I could make my pentode tube amplifier's slam compete with solid state amps, because I couldn't tolerate the compressed, glassy, two-dimensional sound of sand based amps.
A REVOLUTIONARY HYBRID CONCEPT..ALMOST
Dr. Gizmo, when you were probably in a crib, rightfully thought the idea of combing a pentode amplifier with a solid state "amplifier/regulator" made lots of sense, and thought this . before the AIDS plague, when he was trapped in a vortex of sex, drugs and rock and roll. In effect I was creating an ultra simple "solid state amplifier/power supply" to power a tube audio modulator. Such a solid regulated power supply creates an extremely low output impedance that would dramatically improve bass transient response, eliminate power supply noise, and decouple the power supply from any AC contamination..and not cost much.
PAUSE FOR APPLAUDS: Do you see the direct relationship between these experiments with the OTL-1, which is the same concept taken to ultimate implementation.
In the mid-1970s a new generation of high voltage transistors appeared that could be used in high voltage regulators that would be superb for the high voltage power supply of a tube amplifier. Why not use a transistor regulated power supply for a tube amp?
PAUSE: By the 1970s there were lots of "laboratory/industrial" regulated power supplies that used both tubes and transistors, so this was not a new idea. Many industrial tube amplifiers used active power supply regulation, so this wasn't a new idea. So Dr. Gizmo thought if the logic applies to industrial amplifiers, why doesn't it apply to consumer amplifiers? No rocket science here.
To further confound the paradox, by the mid-1970s the notion of using transistors as regulators of small signal triodes was common, and was the key to the new breed of high resolution tube preamps. Why didn't this same logic apply to a big output tube I thought does a tube know the difference?
If, for example my pentode output stage was running on 500 volts DC and I wanted to have, a constant, actively regulated 500 volts, which means that this voltage would not vary no matter how heavy the load on the output stage, I would have to start with 600 volts. The regulator would then have a "reserve" of 100 voltage, behind the 500 volt constant output, to call upon to meet the demands of amplifier. If the power transformer is properly designed, the regulator would in effect create an infinitely stiff output, that would never vary over the entire frequency range. This meant I needed a higher voltage power transformer, which explains why you see two chassis in the pictures of my "hot rod" pentode amplifiers 1970s amplifiers. The outboard chassis holds the new power transformers and the regulator circuits.
In an unregulated power supply it is "normal" to expect the power supply voltage to fluctuate as much as 10-30 percent under heavy load. With an solid state regulator we are talking about less than 1%.
The term "supercharger' works well here, because exactly the same amplifier topology with these solid state regulated power supplies sounded twice as powerful, especially in the below 400 Hz region because the power supply voltage never sagged. Can you imagine driving a car up a steep hill and because your motor is so powerful you don't have to give it more gas to maintain your speed?
You name the pentode push/pull amplifier brand from Audio Research, Mc Intosh, et all, I attached solid state regulated power supplies to all of them and got the type of slammy bass response that I thought only sand based amps could produce with the all of the other benefits of tubes.
And now I have to go further .because it is my job to shred what needs to be shredded.
A PAUSE FOR DEEP PENTODE POWER
Have you noticed that all modern pentode push/pull amplifier used solid state rectifiers rather than tube rectifiers? Thirty years ago the "tweaker" rule was to replace all of the tube rectifiers with solid state rectifiers because they improved the "slam" of tube amplifiers. The reasons that solid state rectifiers became the rule was, as pentode amplifiers become more powerful it was impossible to use a tube rectifier because they could NOT handle the current needed by gaggles of tubes. Even the smaller amplifier used them because solid state rectifiers cost pennies and tube rectifiers cost dollars.
The benefit of solid state rectifiers is that they aren't current limited (because you can always use a higher current rectifier like 50 amps while "normal" tube rectifiers are designed for 1/2 amp or much less ) which means you can use huge power supply capacitors, which draw tremendous current on, turn on, because they look like a dead short to the rectifier. These large capacitors would literally strip and destroy a tube rectifier. You notice that when we use a tube rectifier we use a 100 microfarad capacitor or less, while with solid state rectifiers we can use thousands of microfarads if we want.
So if we need higher current power supplies, that are going to charge huge capacitors, we are going to need solid state rectifiers, and the price we pay is the loss of tonal refinement that is only possible by using tube rectifiers. As you know from my writing: solid state rectifiers produce a nasty spectrum of high frequency hash, and the only way to eliminate that aural contamination is with either a passive "choke filtration" or active power supply regulation..YET..few tube amplifier manufacturers follow this ancient wisdom of making solid state rectification edible.
Why do I mention this? If our design goal is to take the pentode push/pull aural matrix higher, which means taking their power supply design higher, how do we take the slam higher, and not loose the sweetness of tube rectifiers?
ANSWER ONE: Transistor regulators are a brick wall filter to this type of solid state rectifier hash.
ANSWER TWO: Wouldn't it make sense to create two separate, completely independent, power supplies for our pentode push/pull amplifiers?: a solid state regulated power supply for the output stage, so we can achieve maximum slam, and a tube rectified and choke filtered power supply for the front end circuit, so we can maximize the sweet? Why hasn't anyone done this before? Why did God in Her Infinite Wisdom give DR. GIZMO brain damage? Is this some kind of major technical breakthrough. NOT. It is only good thermionic implementation that naturally flows from my passion for creating an optimal tube aural matrix.
ELEMENTS OF PPP BEAUDACITY
My recent article in Listener Magazine on reinventing push/pull delves into this deep. It is not easy thinking in terms of the optimal aural matrix because tradition is strong, so let me give you some concrete examples:
Voltage Amplifiers: The orthodoxy with PPP is to use a 12AX7 because it produces very high gain, and is the least expensive tube. This tube is in the most critical position in your amplifier, yet it is not chosen for its tonal quality, or subtley, or ability to produce complex layers of sound. Have you noticed that the single-ended cult takes their voltage amplifier tubes much more seriously, and for good reason? Why don't designers of pentode amplifiers apply single-ended wisdom to their modality?
Power Supply: This is the ten millionth time I am repeating this..sound quality is proportionate to power supply design quality, and American orthodoxy has not yet caught up with the 1930s..in the 21st century. The soft diffuse sound, the lack of bass transient response, and confused midrange that are common features of PPP is directly related to the absence of stiff power supplies. Rock and Roll demands stupendous power supply stiffness from 400 Hz down because this is the foundation of the music.
The Aroma of Phase Splitters: Every push/pull amplifier has a phase splitter, and there are hundreds of variations. Why is there no discussion of the different aroma of these always less than perfect topologies? Why do members of the single-ended cult care so much about tiny details and the PPP cult doesn't?
The Pentode Power Paradox: Does the same paradox apply to pentodes that applies to directly heated triodes? Are the lower powered tubes more refined? What is the optimal 'screen connection"?
DR. GIZMO'S NEW AURAL MATRIX
A DIALECTICAL THERMIONIC DELICATESSAN
Give Me $45 worth of Parts and I Will
Woodify Your Aural Matrix
The new aural goal of PPP should be SWEET SLAM. Again there is no way for a PPP to have the midrange/tonal refinement of a directly heated triode push/pull amplifier, or, the huge multi-layered sound stage of an OTL..if your speakers are above 95 db efficient, BUT PPP can, if implemented properly, create a deep hot pool of rock and roll magma that will melt you soul.
SWEET SLAM is the optimal aural matrix for PPP because it produces the kind of bass transients that are the one thing that transistor amps do right, and we are able to get the sweetness that tubes produce in the midrange.
What is the point in trying to create a rock and roll aural matrix that is more refined than the aural matrix that is inherent in 99% of CDs? Our mission is to produce the dynamic quality of rock and roll and we want the vocals to speak to us with truth..meaning eliminating the compressed shredded glass sound of transistors. Rock and roll music wants to be played loud like in LOUD, I am having sex with my girlfriend on the couch loud.
Does this seem like a new concept? It is for American orthodoxy, but I developed this aesthetic in the late 1970s, and abandoned it for the development of the Futterman OTL, but then implemented it in the MOSCODE hybrid amplifiers and this is my latest implementation for transformer coupled PPP amplifiers.
Rock and Roll deserve SWEET SLAM.
A PAUSE FOR THE PISSED: Some of you are pissed, and may feel betrayed because you have a collection of rock and roll LPs and CDs that you rightly believe deserve better and you are right. And for those all too rare inputs, you should be listening with more refined tube amplifiers..BUT 99% of rock and roll music is produced for teenage musical taste, in recording studios designed by Complexzilla, whose goal is to celebrate aural discombobularity.
FORWARD: This is the beginning a new design attitude for PPP that takes their primary benefit, which is their high power/cost ratio, accepts their limitations and goes much higher and I don't mean more costly.
SIMPLICITY REDUCED TO ITS BASIC ELEMENTS
REMINDER: An amplifier's power supply is series with the musical signal, and dramatically effects the ultimate sound quality of your aural matrix.
No rocket scientist's brain needed here just understand of gourmet cooking with tubes.
THE SLAM FACTOR: MOSFET REGULATED POWER SUPPLIES FOR OUTPUT STAGE:
How stiff is "infinitely stiff"? The answer is about as stiff as you can get and if we want to create a regulated power supply that is about as stiff as we can get, and if we are ready to pay a price ..to give up a modest degree of tonal/aural refinement, then we have made a whopper big breakthrough that is at least 25 years old, and appears regularly on the latest issues of MJ magazines pages (the Japanese hot rod audio magazine).
By using a high voltage power MOSFET we can with very few parts create a regulator that can handle all of the power of a reasonably powerful pentode amplifier, and has sublime low output impedance, which translates into taking all the flab out of the power supply at lower frequencies. Another benefit of such a MOSFET REGULATOR is that it will also extend the high frequency of the power supply. Improve transient response, improved bass dynamics, lower distortion, lower noise are the benefits, and more .add into the benefit basket decoupling from AC wall weirdness.
The price we pay is obviously relative relative to the sound of tube regulation which is more tonal refined. Relatively speaker transistor regulators have a drier sound because of their harmonic shift up to the higher frequencies.
I am also alerting you that a number of companies sell kits to add this type of regulator to your amplifier, but this is not the optimal route because for this type of regulation to work you need a power transformer that is designed for a regulator.
THE SWEET FACTOR: INDEPENDENT TUBE RECTIFIED/CHOKE FILTERED POWER SUPPLY FOR FRONT END.
You have read my books on the potty. You know that the best strategy for sweetening the sound of a tube circuit is with tube rectification and a choke filter. This means we have two completely independent power supplies, one for the front end and one for the output stage, and because they don't interact the amplifier is in the optimal aural matrix mode. We create maximum sweetness at the front end of the amplifier. How difficult is this to implement? About as hard as opening a can of Bud.
HOW MUCH WOULD IT COST TO
DO THE RIGHT THING?
Wholey Cow let's do the calculations:
The power transformer's B+ voltage after rectification has to be raised 100 volts that will cost about $10.
Regulator parts including power Mosfets, heat sinks, and associated parts will cost about $10
Input/driver independent power supply including tube rectifier and choke will cost about $15
A PAUSE FOR REFLECTION ON WHY
On second thought, don't bother asking the question "Why, wasn't SWEET SLAM, implemented a long time ago?". The only thing that matters is that you know NOW, and you no longer have to muck about in the swamp of aural mediocrity.
A SAD CLOSING COMMENT
The news about the breakup of Nicole Kidman and Tom Cruise is very sad, but understandable given the pressure of being major movie stars. Now you know why I never became a movie star.
MORE TO COME SOON
Sweet Slam: Harvey Rosenberg, 2001
e-mail Dr. Harvey "Gizmo" Rosenberg: email@example.com
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