Technical Bulletin TB-12.

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What makes good tube sound?

Ever since we make and sell tubes, one of the most occurring questions is: 'What tubes must I buy to get ultimate sound out of my equipment'. Now, if people ask the question that way, it is no beginner's question. For that reason, answering it is difficult. Some semi specialist jump into the gap, where real specialist can not give a simple answer, or must even sometimes give an negative answer. Same as in medicine. When the real doctor can help, people go there. If not, they go to people with a lower qualification, to pay a higher price. Some tube doctors have strange theories. In several case you are listening to people with complete lack of engineering knowledge, and they can 'hear' what an engineer can not measure. An experienced technician though, 'can not simply erase the facts from his memory, and replace that information by 'belief'. (This is a quote from Immanuel Kant actually). On the forums, believers team up with each other, and discuss how they hear phase errors above 20kHz. Before you know it, you are in the middle of a dead serious discussion which lacks every technical background. This is not leading anywhere.

Be cautious for black magic.

That can be self-invented treatments, self invented test methods, or extremely tight selected parameters that don't benefit mostly the profit of the seller. Fantasy is set no limits, like CD de-polarizers, direction-sensitive interconnect cables, or 'sound stones' to place near your speakers. If you are searching for these kind of experiences, we have none to offer here. Rather a few very practical things are mentioned here.

Back to the question: What makes tubes good sound?

The answer we have, is based on a simple principle: Sure you heard the expression 'HiFi Chain' before. This is a chain indeed. Sound is passed through very many elements, more then you may be aware. Each has a function, and very few of them have the function to change the sound, like for instance a tone control has.

If one element in the chain that is weak, it ruins the good function of all others. So a chain can not be stronger than it's weakest element. Meaning each element must have equal quality. Let's give an example of a wrong choice. Suppose you have 10000$ to spend, and you spend 9500$ on the amplifier, and 500$ on the speakers. It is obvious that this will not give the best sound for your 9500$. You need to balance the cost between speaker and amplifier. For 'just' 1000$ more you have 1500$ speakers, which will make a big difference, whereas the amplifier of 9500$ or 8500$ will not sound so extremely different. This of course is logical.

When it comes to replacing tubes, the above rule is also valid, but many have learned it the hard way. Suppose the listener has the idea, tubes may sound better than transistors. Then an expensive r amplifier gets replaced by a tube amplifier. Being aware that this is an experiment, the amplifier may not cost much. A 5000$ transistor amplifier gets replaced by cheap amplifier from Ebay, for just 400$ new, including shipment and all tubes. The hope is, this will at least give 'tube sound' not knowing yet what that might be, but when that sounds better, the user plans to buy a more expensive tube amplifier. After a while, they users comes to the (valid) conclusion the sound is disappointing, and the suspected elements are the Chinese tubes. The frustration is very large, when they find out a set quality tubes costs 2x more than the whole amplifier without tubes. So the Chinese tubes are used further, until they get weak. It can take up to two years, and even then, when they get replaced by expensive tubes, the result is only average. This is because in the amplifier are likely output transformers, wound on cores, same as for mains transformers. If you are in a situation like this, better cut out the weak elements completely.

The following happened to me. In 2008, we presented the EML 2A3-Mesh tubes on a HiFi show, playing with a Yamamoto A-011 amplifier, and a set of exclusive horn loudspeakers. Actually build by a person who holds a still valid patent on dipole bass speakers. So when I say great speakers, I mean great speakers! There was a middle aged woman listening to the amplifier, and she returned every day of the show. She came with her husband, and bringing vintage Pink Floyd CD's, asking to hear them, over and over again. I saw she was crying. I asked if she had a problem, but she said she just liked the music that much. ok it happens. Then what she told me, moved me so much, I want to tell this here. The sound was so wonderful, but the reason of her sadness was, she spend 20 years of her life, unknowing such a sound excists. She asked if she could buy the loudspeakers, after the HiFi days are over. Which was not planned for, but it was possible. She was so happy about this, and cried again, because she said she can not get back those lost years of listening to lower quality music. Pink Floyd music is very important for both her and her husband, it is part of their lives. This is a true story.

To my opinion, a well balanced set of tube gear is combined the following way:

1) Begin with top quality tube grade speakers. Requirements to speakers for a tube amplifier are higher than for a transistor amplifier. Such speakers have following properties:

Efficiency above 95dB...100dB.
Small Size and good sound never go together in harmony.
Linear impedance graph. Always ask for one. If the seller says 'huh?', just walk away. Impedance must be 8 Ohms at all frequencies. Since that is never the case, you want to see for yourself how well the designer did his work. 'Linear' means, a line that is straight. No curves like a hopping kangaroo. A non-linear impedance speaker is no problem for a amplifier with feedback, but it is a major problem for a tube amplifier without feedback.
Large surface of bass speakers. The only way to move air mass is by using a moving SURFACE. Too small bass speakers may develop bass volume still, but these introduce distortion at the interface of the membrane to the air. So the membrane moves correct, but the movements are nor the same. The larger diameter the membrane, the less you have a problem with that.
Two bass speakers in parallel is better than one, but not be good as one big speaker of the same surface.
Avoid bass resonance chassis like monkey plague. (The ones with a hole somewhere in the cabinet). Very good is open baffle.
Don't buy any stories about new invented speaker constructions. There are none.
No 'shout'. Often heard problem with high efficiency speakers. Only possible to hear by sound compare and demonstration. Don't let the seller fool you with non-shouting music, like a human voices, or cello play. Also it is kind of mean, to let the user listen to music which by nature comes out of a horn or a cone. Such as saxophone, or trumpet. That makes bad speakers sound good.
Much more difficult is hard rock, even when you don't like it. Bring your own CD's as the speaker demonstrator has such with him that sound particularly nice on those speakers. Also symphonic orchestra with loud crescendos is very difficult for speakers with too small bass chassis. Even if you don't like that sound, or perhaps you do, speakers that can reproduce THIS nicely, sure sound better with soft music as well.
Very large rooms: Take horn driver speakers. A horn driver is a small element, of the size of a fist. On that is attached the horn with screws. So a normal paper cone speaker, attached to some element with horn shape, is technically speaking not a 'horn driver'. Click here, to see a good example of a horn driver.
Very small rooms: Don't take horn drivers. (Some of those can look like a horn, but are not)

2) Connect to this to the tube amplifier

The amplifier must fit to the efficiency of your speakers system! If not, result will be not good.

The tubes have something to do (otherwise they will sound sterile)
The tubes are not stressed (otherwise sound will lack dynamics)
The amplifier should play at sufficient loudness at 25...50% power maximum power.

Don't connect a 2x 50Watt amplifier to 108dB speakers. This will sound sterile.
Don't connect a 2x 1Watt amplifier to 93dB speakers. Unless the room is very small, it will lack bass pressure, and dynamics.
Single Ended amplifiers sound better at low power, push pull amplifier are more suited for high power.
Push pull amplifiers wear out the tubes faster.

3) Put in there the best quality tubes

When you have all the above set right, you have come at this point here. Even a high cost tube will not be overly expensive compared to what good equipment costs, and sure with good equipment you will hear that!

'45 tube' amplifiers

Best sounding tubes are real woven wire mesh tubes. The Chinese produce what they call mesh tubes, but when you look with a lens inside, you will see these are only thin foil with holes punched into it, simulation the optics only. These tubes have nothing to do with real mesh wire anodes.
For the historical EML tubes we recommended mesh only for amplifiers that have a low hum level. With modern versions however, both mesh and Solid Plate are extremely low in hum, and outdo most NOS tubes. The modern versions have a virtual filament Cathode Tap to make this possible. Mesh sound is said to be more transparent, though electrical measurements verify just the same performance.

'2A3 tube' amplifiers

Also here we see the Chinese selling punched Anode tubes, as mesh (See above under '45 tube')
Most recommended type is the EML-2A3 mesh.
You can take EML 2A3-S also, this tube is fully 2A3 compatible, and in case you plan to do so later, it can be biased higher. Because of higher ruggedness, the 2A3-S is very good for push pull, though the wire mesh version is also suited for that, without limitation.

'300B tube amplifiers, recommended tubes

EML 300B. This is our standard 300B tube to replace western Electric tubes, giving the classical 300B sound as original.
EML 300B-XLS. This tube can replace 300B, but is larger dimensions. It has slightly less distortion at higher dynamics still. So this is an upgrade type. For user's words, read 'opinions' from the JACMUSIC web site menu. You will soon notice every fourth positive feedback is about the 300B-XLS, whereas this is the total feedback for all sales, of a very wide product portfolio. This tells it all. It is one of our most successful products.
EML 300B mesh. A specialty for 'connoisseurs'. We do not line up with a famous Chinese factory claiming to have 40Watt mesh tubes. Claiming that is easy, but making that? We say it is impossible. The EML 300B mesh is not 'a 300B with mesh Anodes'. The EML300B is a 520B with mesh Anodes, and like that we could specify it 22 Watt typical and 28 Watt max. It can be put in any 300B configuration though, since the working point is softer at only 22 Watt. So you can replace a 300B with the EML300B-Mesh if you have a way to set the bias at 22 Watt.
EML520B-V3. Yes! It can be used, provided you can supply the higher filament current, and have a way to bias the tube right.

Some items to take care of.

We only sell tubes, not amplifier services, but it is amazing how often such items appear. So please let me put some together here, unsorted.
Imprecise bass, due to damping factor problems. Damping factor is a number, and it is nothing but the specified output impedance of the amplifier, divided by it's REAL impedance. This may be confusing. The specified output impedance of an amplifier, is referring to the speaker impedance that you should connect to this output. So when you see '8 Ohms' printed next to an output, that means you should connect an 8 Ohms speaker to it. Yet the output impedance of the amplifier itself is a lot lower. Perhaps close to zero ohms, when the amplifier has very much feedback. Still the idea is, to connect an 8 ohms speaker to it. This is often an overseen factor: So what is the damping factor or the amplifier. Before we do more numbers.... Why is it called damping factor? That is because a speaker can do two things. First, it will translate the electrical signal into a movement, which hopefully is identical. However when the membrane moves, and suddenly the music stops, the membrane has to stop immediately. Regardless it's movement, though bass membranes are large and heavy. So when they move, they will not stop immediately just by remove the signal from them. There is however something that breaks them. The moving membrane generates a voltage. It is like an electricity generator at that moment. All you need to do, is pull current from this voltage. That consumes energy, (Voltage x Current) which energy is derived from the mechanical movement, and so the movement will stop faster. The amplifier output with zero output signal, connected however to a swinging bass loudspeaker, can pull current from the speaker, because the amplifier has an impedance. So at that moment the amplifier output becomes the LOAD for this electricity generator. A lower output impedance is a higher load. A practical number for the real output impedance of an '8 Ohms' amplifier is for instance 1.3 Ohms. This differs per manufacturer. This value of 1.3 Ohms would give a damping factor of 8/1.3 = 6.2. Some speakers need a large damping factor than others. Such that need very little, are open baffle. Such that need very much are bass reflex boxes. If the damping factor is not enough, membrane movement becomes undefined in the bass range, to some degree. Bass may become too loud even, and sound becomes Imprecise, muddy. If you have this problem, here is a good hint: Some amplifiers have multiple impedance outputs. The real (internal) impedance of the 4 Ohms output is lower as with the 8 ohms output. Roughly a factor two. By connecting the 8 Ohms speaker to the 4 Ohms output, you are doubling the damping factor. If you have still enough loudness this way, you have to try. If yes, this may be a good solution.
Imprecise bass, due to room resonances. Though mechanisms and solutions are another, the bad sound from this is similar. In a room you can have so called standing waves. So at specific (there are many) frequencies, the room will resonate. With a tone generator you can easily find those frequencies. First, of course this sounds bad. These are (multiple) low frequencies that are derived from and added to the music signal itself. Mathematical this is called unlinear distortion. It makes the music sound muddy. So when you have a room resonance at for instance 110Hz, a music tone of 115 Hz, will not make an additional tone of 110Hz appear, but rather that tone of 105 Hz becomes louder, and fully undamped, which is another word for distortion. On the other hand, short low frequency impulses, like from a drum, may make the whole range of room frequencies appear spontaneously. So the room responds with some rumble-like echo which is hard to recognize, as you will also hear the original music. To solve this, all you need is damping materials, and not even very much. Here is a picture of such material. Here is a good company I bought some from. Click on 'recording studio'. I recommend to buy 8 Anodes of 100 x 50cm , 6cm thick. Do not use similar products for packaging purposes, though it is cheaper. The acoustic foam is quite special material. Actually it is not expensive, and you can buy it in nice colors. It doesn't matter where you place them on the wall, they just have to be there. Put some on the long side and some on the short side of the room. You can disguise them as paintings, with decorated cloth over them. The sound will pass through the cloth. After the room is properly damped, not to much and not too little, the muddy bass sound is gone. You should not overly damp the room, then it becomes what is called acoustically dead. Such a room sounds sterile, and you will not like it. For a good effect, you reach the same with few thick Anodes, as with many thin Anodes. So take the 6cm, and then 8 Anodes may be all you need.
Record player is humming. I got this hint from a professional company. Of course hum can have very many reasons. Here is something interesting to try. Unplug the record player from the mains. Well of course it won't play, but is the hum gone now? This is really a test you may not have thought if! If the hum is gone now, you should try it with a high quality mains isolation transformer, such as Lundahl makes. Connect the record player to the mains, with the transformer, and you have good chances the hum stays away. (and of the answer was 'no', an isolation transformer on the record player probably will not help)