Power output of tube amps compared to solid states

Oh Marakanetz. I'm not sure I can help. Believe it or not, I have several oscilloscopes. I also have impedance analyzers, spectrum analyzers and electronic loads. I work in a state-of-the-art electronics laboratory. The reason I said what I did is because I realize these measurement devices are so we can observe simplifications of the real thing. I know it all too well.

To think that a human can build something that would have the capability of human hearing is an ego trip that no one should succumb to. In my opinion. The day measurements can beat the human brain, our demise, and our goal, will have been reached.

1kW of power from a tube as you imagine it, has no physical foundations. Heat generation alone would preclude that possibility. I was talking about what are called "time scales." We have many scales, as much in engineering as in philosophy, ultimately, but all of them fall short of truly representing what we can witness because time effects extend ad infinitum in both directions and thus there is no end to splitting them up into comprehensible slices. Algebraic formulas and measurements occupy only a small part, but calculus covers them all. This was the point Joe so succinctly and eloquently outlined above. One of the tools available to see the remaining parts is called "frequency domain analysis;" the repercussions of which are called "harmonics," which also extend ad infinitum. There is no end to the formulas in the frequency domain. The day I realized all this was mentally liberating.

Classical formulas exist so that we can comprehend what is going on. This is done by throwing out all variables that we deem "unnescessary" because we would otherwise be overwhelmed. The Taylor Series Expansion in calculus points it out very clearly. But are those variables we throw out truly unnecessary? Would they exist if they weren't? Of course not. That is the crux between art and science.

You are free to believe as you like. If your definition of power has no total derivative, then you win. Otherwise, consider power as subject to time scales and you will know what I am talking about. If you would like to understand the mechanisms I speak of in lots more detail, I very-highly recommend Papoulis' book, aptly called "Signal Analysis."

Arthur

Honestly, Arthur, these two you have submitted are among THE all time posts here on Audiogon. For my money, quite possibly, in fact, the best. I'd be more than interested and appreciative if you laid out as much of what you've concluded as you desire, be it here or offline, irrespective of length, depth, or breadth.

As you can see my coming to the thread four days late, I came quite close to missing it altogether. And, the laziness of not reading a thread from beginning to end actually caused me to overlook it completely in my first pass. It was only in bubbling up through the thread to get a point of reference for some of the back and forth that was going on was I lucky enough to stumble upon it. I'm surprised it didn't elicit a waterfall of subsequent discussion. Hopefully, it still may; even if calculus, and mathematics in general, is something we fall far short on as a society at large out of our irrational fear of something that should not to be feared, but embraced.

A few simplistic and personal audio examples that I'm sure most of us can relate to:
1) I used to have two integrateds manufactured by the same company, created by the same designer (if that's of any concern). One was a 120 wpc (hybrid - tube preamp/solid state output) solid state amp, the other a measly 11 wpc push-pull 2A3 tube unit. Apart from such characteristics as tone, (which is actually a quantum leap over the so-called "simple" subject at hand - power), the 11 wpc tube amp walked away from the 120 wpc in what I remember to be every loudspeaker I paired the two of them with. In fact, the order of magnitude difference in rated power seemed exactly backwards

2) That same aforementioned 11 wpc 2A3 tube integrated was also available in a 22 wpc 300B version. Again, obviously, the tale of the tape seemed to make it plain as to who was who. Again, the 2A3 amplifier readily eclipsed the supposedly more powerful 300B model. Any reasonable and average person who didn't read the product spec sheets and relied solely on their own personal being when asked to match amps and numbers in order to assign the power ratings would have chosen the exact opposite of what the paperwork stated

3) A week ago, my buddy and I visited a local dealer to listen to a pair of loudspeakers he was interested in. One of the amplifiers we used in the demo was the Manley Stingray. Initially, we listened in tetrode mode, which provides 40 wpc. As an adamant fan of triode tube operation, I badgered him enough so that at some point, he acquiesced, and we "moved down" to the low rent 20 wpc triode provided. Yet again, in any subjective real world listening test, one would think the ratings would have been the other way around. Triode operation was simply far larger and richer, putting some real meat on the bones and yielding more real world tractable power

4) One question (OK, I lied, this one is neither simple nor clean, and admittedly, maybe I've always missed the boat on this subject...) I've always wrestled with - from the methods we calculate power today, biasing a tube amplifier into Class A operation ALWAYS yields a lower figure than Class A/B operation. Yet this contradicts what would otherwise inherently be obvious (at least, to an admittedly stupid and simple person such as myself) that more current flow through a tube would equate to more (and not less) power. Anyway, my real world example is the Jadis integrateds (again, for those who care, another situation of same company/same designer). The Orchestra Reference is 52 wpc (published specs are usually 40 wpc, but taken from the smaller Orchestra figures) Class A/B, the DA30 30 wpc Class A - both amps using 2 output tubes per side be they EL34/KT77, 6550/KT88/KT90, etc. You know where I'm going here, along the lines of my argument, in my real-world experience with the two, the DA30 is readily the stronger amplifier

Continuing again with the arithmetic/algebra - calculus theme, attempts to correlate the steady state conditions that are the very nature of the measurements of amplifiers heretofore with the dynamic and instantaneously changing phenomena that music (and, the reactive load the partnering loudspeaker presents to an amplifier - something curiously ignored in these measurements) is has, and will continue to, create(d) more problems and confusion than solutions. Along those lines, we often become slaves to such measurements and the machines we have built to implement and execute them which your statement, "To think that a human can build something that would have the capability of human hearing is an ego trip that no one should succumb to. In my opinion. The day measurements can beat the human brain, our demise, and our goal, will have been reached." captures so well.

Then again, living in a world where "watts is watts" and "watts - more is better" is so much less difficult than asking the tough questions that you have, and provides for the quick and easy compartmentalization and subsequent rankings/judgements desired by the customer, salesperson, and (most unfortunately) even, the scientist/engineer/teacher.

My overall point is this subject is far more complex (which we should embrace as a challenge/something fun, and not run away because we feel it's hard work, too dificult/esoteric to understand or just plain scary) than plugging in parameters like Watts, Volts, and Amps into a simple algebraic equation, solving for the one unknown of the three, then going home for the day because we think we're finished. In no way am I saying here that Ohm's Law is any less beautiful, valid, or even appropriate. However, the numbers that we're inserting into the formula when dealing in relationship of amplifier, music, and loudspeaker relationship clearly are.

Wow. Now this is good reading.

Ralph,

Thanks for your response. I am seriously considering giving one an M-60 pair a try. In your opinion, do the Zeros (or other auto transformers) change the sound much?

Great post there Joe. About your comment that Class A operation reveals lower-power figures that expected: You are absolutely correct that theoretically Class A should be able to yield higher power because there is no zero crossing. There are three main aspects, as I see it, as to why in reality it doesn't work out that way - and also how they impact tone because your comments about differences in tone between single-ended and push-pull are actually related.

1) Accurate low frequency reproduction is more challenging in tube circuits that slide into Class B because the power continuity gets broken when no tube is operating. This particularly impacts the low frequencies because they are the ones that need the most power. And they are the ones that mainly have to do with tone.

If I may use an automotive analogy, it is like comparing a manual transmission with a dual-clutch transmission, such as the ones in the latest Audis and BMWs. There is no interruption of power in the dual-clutch setups since there is always a set of plates that are transmitting full power. This is like Class A. But in the other case, you have to put the clutch in and the RPMs drop like a rock as you disconnect the engine (amp) form the transmission (speakers). This is like Class B. The end result is that tone (mainly bass) is much more easily conveyed in Class A operation since the power is always on tap. There is no denying in the world of automobiles that constant power leads to higher performance. Guess which mode of transmission is used in race cars.

2) The actual power ratings are lower than Class AB because of physical power dissipation limits. To operate with a constant bias requires high heat dissipation from the tube's plate. This would be fine except that the cooling medium inside a tube is vacuum, which is as bad as it gets! A vacuum is a terrific thermal insulator since there can be no convection cooling and thus all the cooling is due to "black body raditiation." I have better stop there before I get into the Second Law of Thermodynamics! lol. So yeah, to keep the tube from overheating you have to cut back on the output power. Basically you trade power for bias, which has of course its known merits in addition to this inconvenience.

3) The output transformers in a Class B amp are not designed the same as in a Class A amp. If the amp is Class AB, I am sorry to break the news to some of you but that means it is a Class B amp as far as circuit design goes. Many people feel it is better to say AB rather than B but as far as the electrical design is concerned, there is Class A and then there is Class B.

In a Class A amp, the output transformers have to have an air gap. This means that the core is not made of one continuous piece like it is in a Class B amp. This is due to the fact in Class A you have constant positive DC current in the primaries of the output transformers that should be equal to half the peak output current. In order to prevent the core from "overloading," technically called "saturation," you have to literally cut a slit into the core somewhere so that the excess magnetic field (that goes above and beyond satisfying the core's inherent magentic self-inductance which is what allows it to work in the first place) gets trapped in the air gap. Since air doesn't magnetically saturate, it is a stabilization method for the core.

In addition, this means that a transformer for a Class A amp must be a lot larger than a Class B one because you can't maximize the use of the core since the polarity is always positive, and, the air gap adds its own detriment to the performance of the core.

In a Class B (aka Push-Pull), you don't have to worry about these problems because of what I pointed out in 1) above: the net DC current in the output transformer is essentially zero because the tubes each turn off at the end of their respective cycles. They aren't "on" all the time like they are in Class A.

I feel certain that all these differences account for the changes in sound and tone between a Class A amp and a Class B amp, in addition to the differences in circuit topology of course. If you can live with reduced output power, higher temperatures, higher cost, and higher weight, then Class A has definite advantages. :)

I have two push-pull amps now and I am dying to get a Class A SET because I finally have speakers that can live with their downsides. I’m still in the process of figuring out which one to get. As far as differences between different push-pull amps, that lays in the gray area of performance overlap between designs. Which is better will depend on the type of tube, the power supply design, circuit design, personal preferences, speakers, and room.

As I said before, the sonic results of all these technical details can only be adequately assessed if there is an experienced human in the feedback loop. Only then are all the requisite variables fully taken into account.

Arthur