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Ms.Triode Guild® 2001
Why must men smoke Havana cigars, or debate which cam shaft and carburetor is right for their Cobra, or spend weeks contemplating which dry fly to create for their favorite trout, or which type, brand and weight of bullet to use in our custom made ammunition, or why do we have to go to London to have our suits made on Saville Row, or what brand of silk condom to use or why use grid chokes, plate chokes or interstage transformers?
You know the answer to these questions and it is because we have no choice, if we have been cursed and blessed with refined senses and not every man has this gift and burden which becomes an existential imperative, my dearly beloved musicmaniac bros' ride on and right on..
As you know magnets are becoming more popular I noticed that you can buy them to put in your feet and on your wrist to get the benefit of their healing power. I think I also saw them for sale on QVC and the Home Shopping Network. If women are becoming more sensitive to magnets I thought of a great idea for a new product: Boob Magnets that would keep them from becoming victim of gravity; from sagging Now that we have finished with that subject let's get to the real important stuff .
This has been the year that I have been preaching the importance of you taking your magnetics more seriously .and I started with OPTs because they are the primary "magnetic transformer" in your tube amplifier. Audio Magnetics is a very complicated subject because there are so many variables and unmeasurable qualities inherent in the design process. When you read a text on this subject be prepared for serious mathematics. Because everything in audio is a compromise, it is important for you to understand the price you pay for the choice you make. There is only one place where lunch is free and your are not going to get there until after your funeral.
We are fortunate that the transformer winding art is in a golden renaissance, BECAUSE OF YOUR ASCENDED MUSIC REFINEMENT, and in no small part due to the hot new trend in the recording industry known as VINTAGE AUDIO, which means tubes, which usually means transformer coupling for line level gizmos .or what about the guitar amplifiers? This pro-tube audio renaissance is because tubes are the best defense against the DIGITAL DEVIL.
We have also witnessed the arrival of the boutique transformer winder the man who will custom make your design as a part time occupation often times with very expensive transformer laminates and silver wire for the connoisseur. The recent bad news is that Tango Transformer of Japan is closing up shop, ending a dynasty that inspired new generations of transformer artisans. But weep not the next generation of transformer entrepreneurs in Japan, Europe and America are in full large swing.
I have not yet begun my re-examination of push/pull designs, but let me assure you that designing such a transformer, at a high degree of refinement, is as difficult as designing a state of the art SET OPT and this subject has not been given enough attention in a world dominated by push/pull.
A RICH MAN'S GAME?
As you know from reading my articles about the Lundahl Armada project I am fascinated by "magnetic coupling" which is a term I use to describe using grid chokes, plates chokes and interstage transformers. These all look like small transformers, and they are used in place of either the typical resistor or coupling capacitor .so the first consideration we should discuss is their high cost relatively but not really.
Before I discuss their cost, let me once again remind you that these devices hark back to the primal big bang of audio circuits at the first quarter of the last century because there were no high voltage capacitors and or they saved battery power from the big lead acid battery under your table that was used to power your radio because there were no AC rectifier tubes yet. You can't get more ancient than this which explains why this is the hot modern rage because the time dialectic reigns supreme in transcendent art. This translate into .we must look to the past for higher experiences of beauty, and in a modern culture that promotes new is better, this is anathema and a major bogusity in the audio arts.
My response to those who are repulsed by the notion of THERE IS NO SUCH THING AS PROGRESS IN ART SO FUCK THESE DEADHEADS IF THEY CAN'T TAKE A JOKE because the reality is that, when we properly used, magnetic coupling creates something quite magical and in Nobu Shishido words no explanation is possible or necessary.
GRID CHOKES: As you know, in every triode voltage amplifier, meaning the first stage of your amplifier, which is usually one of the triodes in your dual indirectly heated triode like a 6SN7, or 12AX7, et. al., there is usually a 100K resistor from the tube's grid to ground. When your music input signal, which is a tiny AC multi-dimensional electrical wave, is placed on the electrical potential of the grid, established by this 100K resistor, the grid's relative electrical value changes and this permits electronics to flow from the plate to the cathode thereby creating amplification..gadzooks! Your input signal appears across this resistor which is why it is given such serious consideration. For example I only use an old fashioned carbon resistor in this position because I find that a metal oxide resistor sounds hard in this position.
So why eliminate this 100K resistor, and why does a grid choke sound so much better and different when it replaces one of those tiny resistors? The notion of using a grid chokes was first laid on my brain my Mike LeFevre of Magnequest Transformers because he was making a bunch for a Japanese customer.
A choke is basically a device that has high AC impedance, which means it won't let an AC signal flow through it , meaning it has AC inductance. These tiny little grid chokes, which have virtually no current running through them, typically have very high inductance, which is exactly what we want because, they are the way we set the electrical potential of the grid.
These little precision made magnetic devices are not cheap and will cost you between $30 and $100, which replaces, at most a $1 resistor. Is it worth it? Definitely, if you believe that a Havana cigar has better tone than a White Owl, and there is no SET amplifier that wont benefit, and installing one of these, which is nothing more than removing one resistor and replacing it with this device should take about ten minutes and I am sure will fit in any amplifier.
As Nike, the audiomaniac says "Just do it".
PLATE CHOKES: Let's take a SET amp, which usually has three triode stages: a voltage amplifier, a driver stage and an output stage. The voltage amp and driver stage is usually composed of the two small signal triodes enclosed in a dual triode like your 6SN7. The voltage amplifier must have a high value resistor on its plate to load it or it won't amplify or it can have an active form of load like the constant current source offered by Doc Bottlehead, or the MU Stage, designed by Allen Kimmel, which is a tube constant current source. There are serious debates about which of these technique sounds better, with some claiming that added circuit complexity is detrimental, while others claim superior results.
A plate choke also looks like a small transformer and it is the load for the tube, and it, because it impedes the flow a AC signal, or AC ripple on the power supply offers greater isolation for the tube than a resistor. I remind you that a plate choke must be specified for its electrical value in terms of inductance and how much current it will require to pass. Some tubes are biased to draw only a few milliamps, while other may draw up to 40 ma, and these would require very different choke designs.
Having experienced Lundahl, Bertolucci and Magnequest plates chokes each are different designs and each had different electrical values, and I can assure you, once again, that they are superior to using a high value plate load resistor and again I remind you that connoisseurs debate which type of plate load resistor sounds best .so something is happening here and it is impossible to explain with conventional audio engineering.
You can remove your plate load resistor (which is usually at least 100K) and replace it with a plate choke if there is room for it, in or on your SET, and if you are ready to pay the price..do it.
WARNING: YOU MUST ADJUST YOUR VOLTAGE ON YOUR PLATE WHEN YOU REMOVE YOUR PLATE RESISTOR AND INSTALL A PLATE CHOKE. FOR EXAMPLE IF YOUR VOLTAGE AMPLIFIER NEEDS 60 VOLTS ON ITS PLATE, BECAUSE THAT IS WHAT APPEARS THERE WHEN YOUR PLATE CHOKE IS INSTALLED WHICH MAY REQUIRE A RESISTOR IN SERIES WITH YOUR POWER SUPPLY.
COUPLING BETWEEN VOLTATGE AMPLIFIER AND DRIVER STAGE: The first stage, the voltage amplifier, must be coupled to the driver stage, and my experience is that when possible direct coupling is very desirable, which means there are no capacitors. But this is not always possible, so we must choose either a capacitor or an IT. Again the debate of oil versus plastic capacitors. My vote goes for plastic capacitors when the amplifier is to be used below 1KZ in a biamplified system. If it is a full range amplifier use an oil capacitor to get best tone, but you will sacrifice some bass transients.
In the Lundahl Armada and in other amplifiers I have experimented with using ITs as coupling devices between these two stages and they work but may be going too far over the edge.
SOME COMMENTS ABOUT DRIVER STAGES: The ideal driver stage is able to swing large voltage, which means it is operating at 300V+, has low output impedance, high transconductance, and can produce significant current for a miniature triode. But because paradox reigns supreme we note a debate here because it appears that the more modern TV tubes/dual triodes have superior electrical performance than our classic audio tubes like the 6SN7 so why do so many use this tube? The answer is tone, tone and more tone and the availability of many different NOS brands all of which sound very different. The 6SN7, in a sense, is not a good driver tube, which is why using an IT with it makes such good sense, because the IT un-burdens the tube. I have used a direct coupled 6SN7, with a grid choke, plate choke and IT with truly great results and nothing can be simpler than this circuit.
On the other hand I use the 6EM7, which is a video tube as a voltage amp/driver stage for my "simple" bass amplifiers. This tube is quite different from a 6SN7, and its driver stage has a much lower output impedance, and produces twenty times the current of a 6SN7, and requires a beefer power and filament power supply and a much more robust IT.
Of course we are in a completely different arena when we are using a 2A3 or a PX25 as a driver tube .and what could be cooler?
The reason I have spent so much time discuss "dual triode/octals" is to explain how the Lundahl Armada 4th Wave Modality concept can be applied to simpler and less costly circuits.
INTERSTAGE TRANSFORMERS: One of the revolutionary facets of the DHT SET revolution is the very high IQ dialog that broke out about the quality of drive circuits .a dialog that never emerged in Pushpullville. The only reason this emerged was because we could hear the differences in different types of drive circuits because these ultra simple SET circuits reveal subtle circuit features more than any other type of amplifier. No longer was a 12AT7, 12AU7, or a 6922 good enough. This is another example where our Japanese bros' stimulated the way, because they, more than us, love to listen to the fireflies arguing about drive circuit aesthetics by moonlight.
It was probably Nobu Shishido's article in Glass Audio that ignited the IT fad in America, so before I sat down to write this article I took out my file of Nobu correspondence. You will remember that I was the first to audition the WAVAC amplifiers and remarked how different interstage transformer coupling sounded, compared to RC coupling. You will also remember than Nobu was clear about its benefits but couldn't explain, in a sense, why there was such a high degree of refinement.
In a summary nutshell what Nobu's IT concept was telling us was that we need a very powerful drive circuit one that is capable of large voltage swings and relatively high current which is why he used a triode connected pentode as a driver tube.
Most SET fanatics have rejected the tradition plastic coupling capacitor in favor of oil filled capacitors because oil filled capacitors don't sound like plastic they sound smoother and harmonically more natural so the spiel goes but all capacitors are capacitors, and more and more us are rebelling against their colorations. Those of us who have experimented with direct coupled circuits can immediately identify "capacitor fuzz" when we hear it. The value of "normal" RC, capacitor/resistor coupling is that it is so inexpensive.
So all of us crazies who want more have started to explore IT, which is again, the oldest way to coupling a driver stage to a DHT's grid. It is not easy design a high quality IT, which means wide bandwidth, low capacitance (so it doesn't attenuate high frequencies) and can handle the current with the right inductance. Nobu's favorite Tango IT costs $350 and is no longer available.
An IT can be ordered for your existing driver stage whether it is a single triode in a 6SN7 or some other triode, and wiring it into your circuit is simple, but chances are it wont fit in or on your amplifier. You will note that on every transformer manufacturers web site that they tell you which IT model to use for which driver tube/output tube combination you are using.
WARNING: IT IS EASY TO INSTALL AN IT IF YOU HAVE A SIMPLE DRIVER CIRCUIT THAT USES NO FEEDBACK, WHICH IS NORMAL IN MOST DHT SET SINGLE TUBE AMPS BUT IF YOUR CIRCUIT NEEDS FEEDBACK YOU HAVE SOME SERIOUS CALCULATIONS TO CONSIDER.
DO YOU WANT ME TO ARTICULATE THE BENEFIT OF ITS RELATIVE TO CAPACITOR COUPLING?
I suggest that the reason that the SET thing emerged out of the audio quagmire is for two fundamental music aesthetics: tone and aural wholosity, which these types of amplifiers do better than any other type of amplifier EVEN WITH THEIR GREAT LIMITATIONS AND LESS THAN PERFECT ELECTRICAL PERFORMANCE..in other words what they do right is so profound because they are so supported of real musical values, that the gaggle of things they do wrong doesnt matter.
It is tone and aural wholosity that refined magnetic cream amplifiers in ways that capacitor coupling can not attain.
Magnetic coupling and loading for some reason produces a clear more vibrant and most importantly NATURAL TONE. I hear LESS MECHANICAL coloration. As you know from my writing I believe that TONE IS THE ELIXIR OF ECSTASY, so anything that advances the tonal quality of my circuits become objet d'amour. When switching back to capacitor coupling something is lost; as if a slightly foggy tone filter is added.
Aural wholosity is still a taboo subject in the audio arts because so few speaker systems are able to reveal this quality because of their intrinsic dysfunctional design. When I first heard Nobu's WAVAC amplifier I told him I was writing my appraisal and in his nervous anticipation he called me and put me to the test .and remember he used Tannoy speakers in his home and he asked me the one quality I could detect that was different ..
I told him that I immediately noticed that from about 600 hz down it was apparent that the music sounded more organic, more life like, had better tone and dynamics, but most obviously the entire wave front sound more whole. Nobu was very excited that I could hear these qualities, and he completely agreed.
Having said that are you ready to getting really magnetically freaky? I mean so wiged out magnetically that you will have to take your watch off?
Consider this inevitable and logical 4th Wave Modality thesis Why not choose your magnetics which are optimum for each driver I mean why not design a SET with magnetics that are optimal for upper frequencies and one that is optimal for the lower frequencies like I am doing?
Of course this is possible, and doable
ORDER THESE PARTS FROM LUNDAHL:
GRID CHOKE FOR FIRST STAGE/VOLTAGE AMPLIFIER TO REPLACE THE 100K RESISTOR. #1670 @ $50.75 each
ORDER THIS PLATE CHOKE TO REPLACE THE PLATE LOAD RESISTOR OF THE VOLTAGE AMPLIFIER STAGE OF YOUR 6SN7: #1621 @ $60.25 each A RATING OF 10ma is probably all you need for most circuits
ORDERE THIs INTERSTAGE TRANSFORMER FOR YOUR 6SN7: # 1660 @ 63.93 each..you probably can order a current rating of 20ma.
Of course you can order these devices at higher current ratings for different tubes.
The cost of AIR shipment for two pairs of the above to America is $39.71 and Lundahl takes VISA/MASTERCARD.
PART III WILL FOLLOW SOON
e-mail Dr. Harvey "Gizmo" Rosenberg: firstname.lastname@example.org
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