05 February 2013

Amps: tubes, tubes and more tubes - Part 1


Once Upon a Time there was a guitarist unsatisfied with the tone of his POD X3 Live, that previously substituted a Marshall Valvestate of 30W that never liked and, that one (bad or good) day, decided to try a tube amp. The sound of that tube amp cursed the guitarist and He remained prisoner in Tubeland for the rest of his life. The End?.

After several years testing several amps and trying lot of tubes (or valves), I think it's time to make some reflexions around that cursed bottle.

Without any doubt, nothing can be better than the sensation of the air being pushed by the kick of hot tubes. It doesn't matter how good the solid state amp is, the wonderful that that modeling software works, that wonderful multi-effect pedalboard than can modeling any kind of mythic amp: nothing can sound better than a tube amplifier!.

By example, Amplitube 3 achieves a very nice effect, getting very close to those amp models that it's modeling and, they sound very close to a miked amp recorded in some studio but, there some things that no software can emulate, in any way.

Firstly, the air that amp's cabs move are way more than the air that studio monitors will do.
Loudness (or our sensation of volume) isn't the same, when the air pushed by the amp's cab evolves your body and directly hits you.

Secondly, the feedback. When the gain of an amp is pushed hard, there is some feedback with your guitar that, you could even control and use as an additional effect. Our position respect to the speakers, as well as the kind of guitar and pickups used, make this possible. A controlled feedback was one of the best weapons used by our beloved Jimi Hendrix, by example. Well used, can be an expression tool as interesting as a good Wah.

Alright!. There is some unexplainable magic that can be only found in tube amps, that cannot be modeled by any software, even the most sophisticated but, for this magic to take real place, the tubes of such an amp should offer their best to the amp.

There are a bunch of tube types and models, for pre-amp stages and power stages but, the most spread tube type is, maybe, the 12AX7 (American Specification) or ECC83 (European Specification). Together with the 12AX7, it's often seen some 12AT7 tube and, less often some others.
As power tubes, the most commonly seen are EL84, EL34, 6V6 and 6L6.

What a tube is?

A tube is an old design based around the concept of a triode and, enclosed in a bottle that resembles the old fashioned light bulbs.
The principle behind it is very easy to understand. A triode has 3 elements: the cathode, the anode (often named Plate) and the grid.

The cathode is a metallic plate (or just a filament) that looses electrons when hotted hard. To heat the cathode, the tube uses one more component, named filament (or heater) and, that follows the same principle that that filament that we can find in any typical light bulb. Its highly resistive material transduces the electrical energy into a big amount of heat (it goes so hot that produces light!). The filament is in close contact with the cathode, to transfer the dissipated heat to the cathode. Some cathodes are just filaments.

When the cathode starts to warm enough, it starts to loose some electrons (negative). Those electrons travel inside the tube looking for some positive pole (that has a lack of electrons) and, the anode (or plate) is just that, the receiver of those electrons.

When the cathode is hot enough is when it looses the maximum number of electrons by unit of time (its saturation state). Imagine then, a constant thick beam of electrons traveling from the cathode to the plate, while the tube continues receiving electricity.

This would give us just two states: the tube is off (no electrons) or the tube is on (full flow of electrons), despite of the initial state, when the tube is warming up and going from zero electrons to its max capacity (saturation).

This is how a Tube Diode worked (and still works) but, one more component was designed to regulate that flow, as if it was a faucet, that you can open more or less to regulate the exact flow of water you need at each instant.

This third component is some kind of filament wrapped around some posts, and that follows a spiral pattern and, that stands between the plate (outer and bigger component) and the cathode (inner and smaller component). For how it looks like, it was named the grid.

Usually, the signal that comes from our guitar and enters the amp is directly governing that grid so, the fluctuations in our sound (transduced to electrical flow) are used through the grid to control the beam of electrons that flow from the cathode to the anode. The trick is that the grid can go from zero to values more negative than the cathode and, since negative and negative repels, the emitted electrons go back to the cathode, without reaching the plate. The more negative the grid goes, the less electrons are catched by the anode and the more electrons are rejected back to the cathode.

The interesting thing of a tube is that fluctuations "sensed" in the grid produce proportional fluctuations in the anode, but of greater dimensions. So, if the values seen in the grid move between -5 and +5 V, maybe we can see variations between -100 and +100 V in the anode. This proportion between the input voltage and the output voltage is being called the Gain of the tube.

What means that a tube has a gain of 100?. Well, that means that the output voltage will be 100 times greater than the input voltage, at any instant. So Gain  = output voltage / input voltage and, therefore: output voltage = nominal gain * input voltage.

Imagine a pickup that delivers 400 mV (0.4 V) maximum and, that this value reaches the tube, if the tube has a gain factor of 100, the output voltage corresponding to that input voltage will be 0.4 * 100 = 40V, but since the output of a pickup fluctuates between positive and negative values, the input voltages will be comprised between -0.4V and +0.4V and, the output voltages, between -40V and +40V.

We see that the total variation of the input voltage is of 0.8 V (summing up the negative and positive halves), while the output voltages will vary in 80V. Since the total variation of the output voltage is clearly greater than the variation of the input voltage, we say that there is a voltage amplification.

So, if a tube has a gain of 60 (like a 12AT7, by example), same input values mentioned above will generate the following outputs: -24 V to +24 V (a total variation of 48V).
 tube with a gain of 40 (like a 12AY7) will produce an output between -16V and +16V (a total variation of 32V), etc.

Ok. We got the picture so... why a 12AX7 has 8 pins instead of 3 (one for each component)?.
Because a 12AX7 has TWO triodes packed in the same bottle. So 3 x 2 = 6 pins. And, the other two?. Are used as the positive and negative poles for the filament that heats the cathode (usually named Heater).

All those components are packed together inside a Crystal bottle that needs to be void of air, to allow a better flow of electrons (in the void). When closing the bottle, it always remains some air inside. The final trick is to burn this remaining air, with the help of some chemical component. The Getter is that kind of disk that you can see in the top of the valve (inside) and, that contained the chemical product used to burn the air that was remaining inside the bottle.

Power tubes are, usually Pentodoes and, mount a single triode with two added control grids (suppressor and screen), that were designed to solve some issues that were detected in triode designs (as capacitancy and other issues).
1 triode + 2 grids + 2 poles for the heater = 7 pins, but Pentodes usually have 8 to 9 pins. I don't remember for what are the others. Probably, the octal design has a common negative for each additional grid, while in the 9-pins design, each additional grid has its own negative pin.

The tube: that delicate thing

Every material used for each component, including the flash, affects the way a tube works and, any unwanted impurities that mixes components can affect the way a tube works. And, how a tube works determines how our amp will sound, at the end.

The quite well artisan production of a tube makes all them different. Tube specifications fall into a very variable range (depending on the Maker and Model) and can have a big impact in our tone. By example, a tube that theoretically had to have a gain of 100 (a 12AX7),  and have just an slightly lower gain of 96 is missing some of the total voltage variation that the amp designer expected in his design.
In my opinion, voltage is very related to dynamics, the wider the voltage variation, the more dynamic the sound is, so we are loosing some dynamics, in that case.

Myles Rose has reviewed several batches of several makers and models, taking notes of their technical values measured for each specification and, found some models more consistent than others and, some variations around a 20% below specifications. That could mean to have a tube delivering a gain of 80 instead of the expected 100.

The tube, during its short or long life, its suffering a real torture. The structure of the filament and rest of elements deteriorates in a faster or slower way, depending on multiple factors: from the materials of each component, to the way tubes were biased in the amp, to were they are placed and, how hard are subjected to mechanical stress.

The three components of each triode are, usually mounted on some structures named spacers, that dilate with the heat and enter in contact with the flash, absorbing some of those vibrations and, avoiding that those are being actualy transferred to the triodes.

You never know which will be the life of each tube. Even same maker / models can last very differently in the same amp and same spot. Some spots are harder.
By example, power tubes often last half the life of a pre-amp tube but, the PI or Driver tube (part of the pre-amp) lasts more or less the same as the power tubes, because those are the most stressed tubes in the amp.

If the tubes are inside a combo, the speaker is electromagnetically affecting the tube and, worst than that, the speaker is kicking waves of air that hit tubes hard, what can make that some parts go lose, introducing microphonics issues.

Well, you see, a tube is some kind of art and, every single one, even being very similar to others of the same batch, is somewhat unique. The bad thing is that we don't even know how long it will last, even being specifications-correct.

That kind of rawness and lack of perfect linearity is probably why tubes have some magic that transistors haven't. Each tube creates its own functional noises, its own set of harmonics and, grain and type of distortion. They have a "signature" sound, indeed.

NOS and New Production tubes

If you still didn't heard or read the term NOS, you will, for sure.
NOS means New Old Stock and, refers to those tubes that were produced during the Golden Age of tubes and that were remaining in their original boxes, laying on bins of certain stores (or military surplus depots).

It's paradoxical that the new production tubes cannot reach the same consistent specification values of tubes that were produced 60 years before. Everything seems to be more evolute nowadays, in terms of tools and production techniques so, what's the issue?.

We need some perspective to analyze it. During the '50s and '60s, tubes were everywhere, in TV sets, radios and many many other electronics devices.
When the transistor appeared, because of it`s small size, reliability, cost and more linear behavior, it started to replace the tubes in each existing design. In fact, a transistor is able to amplify our guitar signal with higher fidelity than any tube. A high fidelity means that it doesn't introduces any kind of distortion and, that the amplified sound is some sort of a resized clone of the original sound.

The big business that was to produce tubes, was starting to be impossible to maintain, due to the lack of demmand. Therefore, the big factories that were producing tubes in USA and Western Europe closed.
Only some factories remained in the old Sovietic Union., since they weren't affected by the offer-demand law of capitalism.

Audio is a very curious world. The perfect work of a transistor made the sound more mechanical and less attracting to the human ear. It seems that the magic was in that several distortion forms that tubes were introducing in the sound what made them really attractive to our ears, sounding more musical.

Musicians wanted to go back to tubes and, Audiophiles wanted also to see their loved tubes pushing their expensive high fidelity sound systems. So, they started to get some tubes from those Sovietic factories or Military depots. But, those tubes were sonically very inferior to tubes that were produced in Western Europe or USA. Maybe, they were absolutely correct for Military applications but, they all sounded sterile for musical applications.

Those musicians that still had those vintage amps that delivered the most of tones we can hear as recorded today, started to be in the need of replacing their old tubes and, went totally disappointed with the sound of those Rusian tubes and, started to search for NOS tubes everywhere.
That raised the prices of NOS tubes and, lot of people made a lot of money with all this.

NOS tubes (at least, the ones aftersought) already disappeared from the scene and, a new kind of tubes was sold as NOS. Many people started to rip old gear, like old disk players, radios and, any other kind of electronics device powered with tubes (as organs) to get one tube of that historic golden period and, they started to sell them as NOS, when they were not new anymore (they were already used in that device).
Those made still more money than the first ones and, the bad thing is that lot of people wasted their money in a tube that was already worn, or not delivering the best tone, or that lasted short.

There was a big gap of time were the only available New Production tubes were sonically very inferior to NOS tubes but, fortunately, some companies decided to invest in the remaining factories and, enhance the tubes to reduce the gap against NOS tubes. This was the case of Electro-Harmonix, that invested in New Sensor (Russia) or Ruby Tubes, that invested in a Chinese factory.

Nowadays, they are some New Production tubes that sound quite well the same as NOS tubes or, at least so good that you don't feel in the need to go for a NOS tube and pay the high difference in price against the small difference in sound. Reliability and Production Consistence has been enhanced, also, while prices are way lower so, we are again in a new Golden Age or... a Silver Age?.

Who produces tubes?

If you are in the market for a tube, you will see lots of brands and lots of models within each brand but... are there so much makers?.
The truth is NOT. Tube Makers (that produce tubes for musical amps) are really very few, we are talking about New Sensor (Russia), JJ (Slovakia) and Sino/Shughuang (China) and, eventually, EI (Serbia) and Svetlana (Russia).

It seems as if each Amp Maker had its own Tube Production Plant, since the tubes that came in their amps have their named labeled (Marshall, Mesa, Engl, Koch, ....). All those tubes come from one or more of the few factories mentioned above.

There are lot of tube stores that sell their premium tubes with their name (TAD, Groove Tubes, Watford Valves, etc...), don't they have their own production plant?. NOT, they don't. They just purchase batches of tubes, test them and relabel the nice ones under their own brand name.

To increase the confusion, New Sensor bought the name of very well established tube producers of the golden age and, it's producing tubes under several brand names: Sovtek, Mullard, Genelec, Electro-Harmonix and Svetlana, are some of those brand names.
New Sensor is an American company that produces their tubes in russian Reflector's factories. One of that plants, named Xpo-pul is producing tubes under the name Svetlana but aren't the tubes really manufactured by JSC Svetlana, in Saint Petersburg. Since New Sensor bought the brand name, only New Sensor can sell tubes under the Svetlana name in USA and Canada. But, JSC Svetlana is still producing the real deal, the winged S and winged C tubes and, its selling those tubes without the brand name but, with the winged S (preamp) or winged C (power)  logo. The Winged C EL34 is the most appreciated tube for Marshall amps!.
JJ was Tesla-JJ in the past and, is producing now all their tubes under a single brand: JJ.
Ei produced tubes under its own brand. It seems that factory closed in 2007 and, according to those who experienced that tubes they were the best sounding ones but, didn't lasted long sounding good and, they presented a high ratio in microphonics issues.
Shunghuang is producing no-branded and rebranded tubes. It's the factory that can produce the tubes you want, according to your specifications (usually called STR, like the TAD EL84-STR, by example) and labels them with your name
As any Chinese factory, can produce from real crap to the highest quality product and, it all depends on how much do you want to pay them. They have a dedicated high fidelity brand of tubes, with very high price tags and, they produce the cheapest tubes at same time.
Anyway, chinesse tubes are going everytime better and are really affordable. The 9th generation of chinesse tubes is really good, if we rely in Myles Rose.

There was one more factory in China, I think that drived by Ruby Tubes but, that company brook and, the related Chinese factory isn't producing those tubes anymore. Since they aren't producing Ruby Tubes anymore, those have become NOS tubes!!!. And, since they produced one of the finest 12AX7 tubes, they are aftersought, nowadays.

Paradoxical world, tubes world!.

Some videos

I think this couple of videos about a tour for the Ei Factory can be of your interest.

This one is a complete manual process of a high audio tube type. Since components are bigger, it's easier to understand what was written above.

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