| runeight |
Since I have come back to vacuum tube audio in the last several years, I am fascinated by the concept of tube rolling. I have heard both sides of this issue expressed. Maybe some of you guys can give my your further opinions on this subject. :) If you all have done this before, then by all means stop this before someone gets hurt.
When I was growing up, tuberolling was unheard of. I assume that this is because the rest of the components in the system (transformers, speakers, caps, etc.) were so poor that the differences between tubes could not be heard. Or is it maybe that tuberolling actually has no effect at all?
Let me offer some structure that makes sense to me. Please help me understand why tuberolling works.
A vacuum tube is defined by a very small number of physical characteristics. These physical characteristics, in turn, define the tube as a circuit element. I think it makes sense to divide the physical characteristics into two categories, first order and second order.
These are the first order characteristics that I am aware of:
1. The actual physical dimensions of the various elements (plate, grids, cathode).
2. The geometries and spacing of these elements.
3. The emissivity of the cathode (that is, how many mA/square-mm at what temperature).
Now a tube has only two circuit charactisitics that matter in audio: its interelectrode capacitances and its behavior as a voltage controlled resistor. So far as I know, these three first order characteristics almost entirely determine a tube's circuit behavior, its capacitances and resistances.
There are some second order characteristics too:
1. The actual materials used in construction.
2. Small structural features, such as ribs on plates.
3. Gas in the envelope (which becomes a first order effect if there is too much or if the tube is designed to contain gas).
4. The way the emitting material is layered onto the cathode surface.
5. Whether the cathode is directly or indirectly heated.
There may be others of these.
Now, it seems to me that two tubes of identical physical geometries with cathodes of approximately the same emissivity, must exhibit the same electrical characteristics. There is no way that I can think of that they can behave otherwise.
From the circuit's point of view, it doesn't matter what the tube looks like internally, all the circuit sees are the capacitances and resistances. So, two tubes of identical physical characteristics should sound exactly the same because they produce the same electrical behavior.
OK, so what? Well, let's take two tubes from different manufacturers. They may be made somewhat differently. But, if they behave identically as capacitors and resistors, then how can they sound different? That is, if they display identical plate curves and identical interelectrode capacitances, then how can they sound different since their circuit behavior will, must be identical?
OK, suppose they don't have "identical" curves? Well, if they are the same type of tube, the curves should be within some tolerance range. And if so, what exactly changes anyway?
If tubes were perfectly linear there would be no discussion, because there would be no distortion. But they are not. So, it must be the deviation from linearity that defines any particular tube (what else can it be? except for the capacitances and current handling capacity which I'll get to presently).
Two tubes of the same type, made differently, but with nearly identical plate curves must, therefore, exhibit nearly identical distortion characteristics. In fact, unless one of the tubes is just plain bad, my guess is that the differences in distortion would be audibly undetectable. Are you guys actually hearing these differences? You may be and I truly admit to being very, very far from an audio expert nor do I have wide experience with lots of tube amps. But I would like to know how you hear them.
Do the second order characteristics change anything? Well, if it's the same tube type how can they (unless the tube is bad or failing)? The only possible effect might be actual materials and small physical features. I don't see how the materials could have any effect if they are chosen properly for conductivity and durability. And, I don't see how small scale differences can matter. For example, plate ribs can't possibly change a tube's behavior. By the time electrons reach the plate they are moving so fast that a millimeter is irrelevant (or so it seems to me).
OK, so then the question is, do tubes of different types sound different? Well, doesn't it depend? If the circuit truly exhibits the nature of a tube's plate curves and capacitances, then the distortion characteristics will be different. Can you guys actually hear this in a properly designed amp? :xeye:
And finally, for this post, the current handling capabilities between tubes is an obvious difference that I think everyone understands better than I do. This not only affects power delivery but speed, that is, the ability to charge the load capacitances fast enough for audio (say from 20Hz up to 300KHz). But, two tubes of the same type, if they measure the same, should do both of these things the same and so should "sound" the same.
OK folks, I am standing in front of the target with my arms wide . . . . . . . maybe I should go back to the CCS thread. :goodbad: |
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| SY |
It gets much deeper than that, but to put in into perspective, you can have FETs with the same part number, same manufacturer and even the same batch show Idss and Vp spreads of 3 or 4 to 1. So we're not doing too badly with the real tolerances of tubes.
Some "rolled" tubes aren't even the same nominal part number. For example, there were a lot of 6DJ8s around that were actually relabelled 6ES8s.
There's a lot of myth out there, much as with other aspects of audio, but there are some real differences, too. A quick look at 3 or 4 different 12AX7s will make you appreciate this; I've got three examples here which don't even look vaguely alike inside. The fact that they all have roughly the same characteristics (to first order) is miraculous. The fact that they do function differently in real circuits is understandable. |
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| Sch3mat1c |
Oops, that's a can of worms my friend... :rolleyes:
Scientifically, the way a tube is used is its electrical characteristics. So any actual in-circuit behavior can be measured, as you observed (distortion, gain, frequency response, etc.). Any variations can be narrowed down to the specs you mentioned, plate curves (which cover well over the used range, allowing tight matching if you're really picky) and capacitance. Now really, if these are equal, and behavior depends on this, then there can't possibly be a difference. But apparently, there is! (Although I can't say I've heard of any tests, blind or not, involving precisely matched tubes of different contruction and brand.)
Overall I say it's all in your head. The human brain is suggestible, and if one believes that a particular modification (be it new equipment, tubes, wires, whatever) will improve it, it indeed will. And note also the "it was expensive, it damn well better be worth it!" effect on very expensive things *COUGH*cables* will have a similarly strong effect.
Personally, I can say that several amps of mine, speakers and other combinations can sound good for up to a week, but after the novelty wears off it sounds like **** again. Probably the mental effect of the effort of arranging, since I tend to do things as free as possible...
I can't say I've noticed any differences while rolling tubes, probably because I'm too sceptical, err scientifically-minded.. :D
(I mean, except for 12AU7 vs. 'AT vs. 'AX in my preamp, but that's the differing gain and plate resistance affecting the tone stack.)
Oh, and not to mention rectifiers. Besides voltage drop and supply impedance, well you know where this is going.
Tim |
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| janneman |
Eh, what the ****** is "tube rolling"???
Jan Didden |
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| Sch3mat1c |
Subbing in different brands of tubes in an amp.
Tim |
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| analog_sa |
| quote: | | Eh, what the ****** is "tube rolling"?? |
Seems to me this will be a discussion of tube trolling |
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| janneman |
| quote: | Originally posted by Sch3mat1c
Subbing in different brands of tubes in an amp.
Tim |
OK, thanks. Still have no idea why it is called rolling, but that's OK.
Jan Didden |
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| Pjotr |
Yes at first I was thinking of a new gimmick to improve the sound of tubes by first rolling them over the floor to run them in mechanically :clown:
But no joking, accuracy of mechanic dimensions is very important for the electrical behavior of tubes. Spacing between cathode, grid and anode directly defines Mu. How much are these elements // to each other? Also how even is the spacing between the grid wires? Uneven spacing of the control grid acts like many different tubes with different S in //. Further is the anode coated to reduce secondary emission? Idem for the material of the grids. And so on ...
It is clear to me that tubes from different brands differ slightly from each other.
Cheers |
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| Positron |
I can't remember all that was mentioned in the first post, but, and not necessarily in order.
distortion
gas in tube
curves
Materials
Materials makes a big difference in the sound. I just recently saw a tube ad that actually uses Nickel for the plate. Nickel will sure influence the sonics.
Different brands and years can sound different. Sometimes, tweeking the circuit is all that is needed to make the component sound the same, sometimes not. |
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| Sch3mat1c |
Don't forget:
| quote: | Originally posted by runeight
Let me offer some structure that makes sense to me. Please help me understand why tuberolling works. |
Anything real and measurable can be lumped into parameters (dimensions, materials, etc.), namely plate curves and frequency response.
Tim |
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| Pjotr |
Hi,
Don’t forget the quality of the isolation between filament and cathode for indirect heated tubes. It largely affects noise behaviour. Also how sturdy are the elements mounted: Microphony with the possibility of acoustic feedback.
;) |
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| Sch3mat1c |
Something Colt knows well now! ;)
However, that's a sign of bad design. A good circuit will have bypassed cathodes (shunting H-K insulation-coupled noise to ground) and either a 'hum balance' control, floating heaters, and/or DC supply.
As for microphony, that's a good question that should be investigated... I might have to take the most microphonic tube I can find and use it as a mic on an amp... yes that sounds good... :)
Tim |
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| PRR |
> I just recently saw a tube ad that actually uses Nickel for the plate.
Nickel is the most commonly used material for plates (in "small" tubes such as nearly all audio hi-fi tubes). I'm not aware of anything else that is commonly used in small tubes. Graphite is used in a few very heavy duty tubes.
The only thing the plate does is catch electons. They fly into it at high speed. It does not have much say in how they hit, except that its voltage field sums with all the other voltage fields in the tube to affect how many electrons leave the cathode.
The nickel is almost invariably coated to increase thermal emission and to reduce secondary electron emission. That coating may have an effect on tube parameters, though when working well inside max ratings it should be small.
Runeight, I've never heard a difference in "good" tubes working in the linear range. I have not listened very hard. I tend to favor high-feedback designs where tube differences should not matter.
When you take a tube to extremes, such as in guitar-amp duty, you will find that saturation and cut-off curves do vary a lot with "small" changes in tube construction. In a real tube near "cutoff", the grid wires are passing no current but some is leaking around the grids and the grid support wires. "Small" mechanical differences are then the largest factor. In saturation, grid wire spacing (and in multi-grid tubes, grid wire alignment) can make measurable differences. I have little doubt that guitarists "using their amp" as a tone modifier can hear differences bewteen one 6L6 and another 6L6.
The 12AX7 is a special case because its grid wire is "too close to the cathode". Under most operating conditions, the grid sits in the fringe of the cathode electron cloud. Spacing is very critical, and there are several ways factory tooling can try to hold the critical dimensions. The result is very measurable differences in the kinks near cutoff (which is near the normal operating point for most 12AX7 circuits) and in grid current variation with grid voltage.
There are random flaws that are uneconomic to control. Noise voltage is very hard to minimize. To a first approximation you purify your cathode coating. But the rare earth oxides are complex chemicals and never totally pure. And if you get it very pure the noise may increase: some "impurities" reduce noise. You select your sources and stir the pot well, and still each tube comes out a little different.
Heater-Cathode insulation is ceramic, a clay-paste baked hard. IMHO, if it isn't "perfect", the tube is ****. Yes, there have always been **** tubes and maybe more now than ever. Yes, a few designs (split-load phase inverter) can get in trouble from H-K leakage. Most "good designs" will absorb any reasonable amount of H-K leakage without any ill effect.
What goes on at the cathode interface rivals solid-state theory (in fact it IS "solid-state" theory, only it is a solid/vacuum junction where the solid is on the verge of being liquid). Except a silicon-chip is simple compared to a thermonic cathode. Much of that complexity is masked in negative-grid (actually non-arcing) operation, but the ear is a fabulous analyzer and may be hearing some of the chaos at the cathode surface.
Tubes are fun. If you take it much more seriously than that, they can be a major pain in the ear. |
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| fdegrove |
Hi,
What most people seem to forget is that it's the cathode emitting the electrons and the anode's attracting them.
Differences between tubes of the same type aren't all that subtle either but can often be revealed when curves are traced.
Indeed, different materials make for different sounds I think the one Positron is referring to is something that looks like Chromium.
In Europe we had some 6189s and 12AX7S types made in France that looked like that but never sounded any good.
Then there's the mystery of the mesh plates, the best EF86s I ever heard invariable we're made with mesh plates.
On paper it's like trying to catch electrons with a fishing net but somehow they all manage to sound great.
Does anyone know what the coating is made of on those black plate small signal tubes? It looks like a graphite coating but is it?
Those are often fine sounding tubes too IMHO.
Most people in the tube dealing business will confirm you that 75% of their requests are brand specific. I can't imagine all of their customers being lunatics??
Cheers,;) |
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| SY |
| It's a metal oxide- I think molybdenum. |
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| PRR |
> there's the mystery of the mesh plates, ... it's like trying to catch electrons with a fishing net
No, more like trying to catch flies with a fishing net soaked in honey. They find it.
In most normal circuits, the Plate's positive voltage "sucks" any electrons that come near it. Even the ones that pass through the mesh have no place to go except to turn around back to the plate.
> 75% of their requests are brand specific. I can't imagine all of their customers being lunatics??
Of course they are not all lunatics. But I could believe 75% are, well,,,, not "lunatics" but looking for a Known Brand, or looking to NOT get some chinese junk.
I know several large tube vendors who don't promise you any specific brand. You trust them to pick good tubes. |
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| fdegrove |
Hi,
| quote: | | No, more like trying to catch flies with a fishing net soaked in honey. They find it. |
But of course...how could I have missed that.
I must look pretty stupid to you by know....quite likely I am. :D
| quote: | | Of course they are not all lunatics. But I could believe 75% are, well,,,, not "lunatics" but looking for a Known Brand, or looking to NOT get some chinese junk. |
Having run a business like that for about 8 years I can only say that 75% was a deliberate understatement; most customers were very specific and knew exactly what tube or brand was good sounding.
I could run miles of posts just telling about tubes, tube manufacturers and a lot of prejudice along with an interesting view on how the industry works but that's a little over the top.
Fact is though, most people can hear the difference between a flake and a sunshine.
Let's roll on,;) |
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| Positron |
"The only thing the plate does is catch electons. They fly into it at high speed. It does not have much say in how they hit, except that its voltage field sums with all the other voltage fields in the tube to affect how many electrons leave the cathode."
Actually the plate does more than catch electrons. It use to be that some tubes used copper in a sandwich to conduct heat away from hot spots, or in beam tubes, to the portions of the plate that didn't get struck by electrons.
A more important mission is that the plate carries current (the electrons that strike it) to the lead, to the pin out (like a wire). That could be a half inch to two inch length, depending on the tube. Nickel will sound quite different than if copper could be used.
The ad mentioned only that the plate was nickel. That seemed odd to me. |
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| runeight |
Hmmm. . . . so much information . . . .
| quote: | | Yes at first I was thinking of a new gimmick to improve the sound of tubes by first rolling them over the floor to run them in mechanically |
You know, Pjotr, that's what I actually thought when I first heard the phrase! I kept wondering if the audio community had lost its mind. Then I discovered what tube rolling really is and then I was sure it had lost its mind (just a joke folks, really).
| quote: | | Don’t forget the quality of the isolation between filament and cathode for indirect heated tubes. It largely affects noise behaviour. |
Yes, I forgot about the noise characteristics. I think PRR mentions this too. But, although noise may affect what else is in the signal, I consider it to be a secondary effect. Meaning that the tube's basic circuit characterstics are not affected by its noise generation. However, certainly with two identical tubes, the one with less noise would be preferable. But, this isn't usually what people mean when the talk about "sonics".
| quote: | | The 12AX7 is a special case because its grid wire is "too close to the cathode". |
etc. Yes, I see this. Another way to say it is that when the dimensions and spacings are very small, then even very small errors in electrode location can have a big impact because they comprise a much large percentage of the dimension. That is, if the plate is 50mm from the cathode a .5mm difference in tubes may be unnoticeable, but if the plate is only 1mm from the cathode a .5mm change is a radical change to the tube. My guess is that in this case, the tube curve would be very different. And so, this wouldn't be the "same" tube, even if it were labelled the same. But, I see how this matters.
| quote: | | Yes, a few designs (split-load phase inverter) can get in trouble from H-K leakage. |
Got it. But, in this case, the H-K leakage changes the resistive behavior of the tube and so it doesn't look like the same circuit element as a tube with no leakage. Correct?
| quote: | | Much of that complexity is masked in negative-grid (actually non-arcing) operation, but the ear is a fabulous analyzer and may be hearing some of the chaos at the cathode surface. |
I am willing to believe that this may be true. Do you mean the noise characteristics or something else?
| quote: | | Differences between tubes of the same type aren't all that subtle either but can often be revealed when curves are traced. |
I absolutely agree with this. If the curves are different enough, the tubes are different and may sound different. But, I believe that this effect is much less pronounced than the claims that are made. After all .02% THD is .02%THD, isn't it? Even if it's created by two different tubes? Same for IMD.
| quote: | | I could run miles of posts just telling about tubes, tube manufacturers and a lot of prejudice along with an interesting view on how the industry works but that's a little over the top. |
I would like to hear about this if you have time.
| quote: | | Indeed, different materials make for different sounds I think the one Positron is referring to is something that looks like Chromium. |
I am having a hard time with this one. If the metals are sufficiently conductive and they have, more or less, the same secondary emission characteristics, then how can this be so? If tubes have the same resistive/capacitive behavior doesn't the circuit see the same thing in both cases?
| quote: | | Runeight, I've never heard a difference in "good" tubes working in the linear range. |
This would be my guess, although I can't claim up-to-date experience to say so.
| quote: | | A more important mission is that the plate carries current (the electrons that strike it) to the lead, to the pin out (like a wire). That could be a half inch to two inch length, depending on the tube. Nickel will sound quite different than if copper could be used. |
Do you think that for different, but suitable metals, the change in resistance here will actually change the plate curves? My guess is no, but I have never personally measured it, even when I was smashing pentodes and taking them apart.
Well, you all (what we say in Texas is, y'all) have been most gracious in your replies.
Does anyone have measurements that show two same type tubes of different manufacture with very close plate curves actually sounding different? I would really like to know. As I said in another post, there are always new things to be discovered.
:bullseye:
PS - dear moderators, can I get a smiley face with a cowboy hat please? |
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| SY |
| quote: | | I kept wondering if the audio community had lost its mind. |
Look at the $99 jars of rocks or the $200 magic hockey pucks and you'll come to the inevitable conclusion.
Regarding materials, different metals (and different surface treatments) have different permeabilities, dependences of resistivity with temperature, different work functions, different surface energies and best of all, many plates are made of different layers of various materials, adding construction variables.
Then there's geometry- for a given mu and gm, you can trade off wire diameter, pitch, length, and spacing- and it's easy to find differences in these from brand to brand. If one 12AX7 has a 1 cm long plate and another has a 2 cm plate, one might expect to see that the internals are different. And that can (and does) result in the characteristics' curvature being different, not to mention interelectrode capacitances.
You hit on all this obliquely when you talked about two tubes being different despite being labelled the with the same part number. If you want an easy, measurable way to see the variability in measurements (and indisputable sonic impact), build up a small gain stage with passive EQ. Then change tube brands and see the effect on frequency response. |
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| runeight |
| quote: | | Look at the $99 jars of rocks or the $200 magic hockey pucks and you'll come to the inevitable conclusion. |
I must admit I did find some of these things, shall we say, unusual?
I agree with your comments for sure. But, I would have to say that all of these variables must add up to the tubes acting differently as circuit elements. That is, because they are made differently, they must exhibit different plate curves or different capacitances to sound different. If they don't, then they must behave electrically the same and sound the same.
I would say even further, that it is possible to make two tube with different internal structure to have the same plate curves and capacitances. They will look different, but it seems to me that they must, nevertheless, sound the same. No?
This is a good point though, which leads me to ask: how much different can a tube be from its "nominal" characteristics before it is no longer that tube.
In other words, if I'm building a 12AX7 don't I have to try to hit the nominal plate curves and capacitances (within some acceptable delta)? If I don't and I miss by a lot, then can I claim to be manufacturing a 12AX7? (Although I might anyway).
Now, if part of the tuberolling business is selecting out tubes that are grossly improperly manufactured, then I can see why folks would do it. But then, they're not rolling tubes of the same type anymore, they're selecting from several different types of tubes with the same label to find the one for which the circuit was originally designed. This I believe. |
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| SY |
Tubes have no sound, only systems employing circuits using tubes can be said to have a sound. And if the curves are the same, the noise is the same, and the microphonics are the same, exchanging tubes will not result in the sound of the system changing. If those factors are different, there may or may not be a change in the sound of a system, depending on overall design.
| quote: | | how much different can a tube be from its "nominal" characteristics before it is no longer that tube. |
Aha! A Platonist! |
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| DrewP |
Folks, my experience of tube rolling is very limited but also very recent (within the last month).
I had the oppourtunity to visit a friend running a Sony SACD player into a custom built preamp using 6CG7's, then into a custom built single ended power amp using 13ei's as the output tubes. Speakers were Vienna Acoustics (Mozarts I believe).
The preamp used an offboard power supply and all equipment was on racks.
When I arrived the preamp was using a pair of vintage Mullard 6CG7's, later they were changed to vintage telefunken 6CG7's and then to a apir of new Electroharmonix 6CG7's.
These were the only changes made to the system and the tubes were subbed back and forth a number of times on a range of music (Kind of Blue being the main reference disc but female vocal used also)
The differences were not subtle.
To broadly categorise:
The Mullards had a more smooth and pleasant midrange, slightly rolled off treble and a bass region that was both slightly recessed and loosely controlled. a rea "classic tube" sounding tube.
The Telefunkens were tight, controlled and precise. Certainly "brighter" in sound with a far more precise bass. On some recordings they could be accused of sounding harsh. a more intellectual and less emotional listening experience than the Mullards.
The Electroharmonix were a real suprise, especially as some of their more recent concoctions have recieved a fair amount of praise. Bass was extremely overblown and substantially uncontrolled, midrange and treble detail was muddied. Very first initial impressions following on from the Telefunkens were that we had returned to a musical sounding tube but this initial impression quickly changed to a feeling that something sounded very wrong.
Remember that plate curves only show steady state conditions.
How a pair of plates spaced apart with electrons wafting between them can exhibit an altered frequency response i cannot comprehend, all I can say is that they categorically do.
Apologies for the lack of scientific data to add to the discourse apart form my subjective impressions.
drew |
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| dhaen |
| quote: | Originally posted by runeight
snip..
I would say even further, that it is possible to make two tube with different internal structure to have the same plate curves and capacitances. They will look different, but it seems to me that they must, nevertheless, sound the same. No?
...snip |
Compared with the norm, I've seen some valves of alternative construction, that were electrically identical, while others that were visually identical were way off.
I think you can only go so far on this though. As frequencies rise, C & L both become more significant. There's not much "cosmetic" variation in valves designed for UHF and up. There are also fewer "equivalents". |
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| analog_sa |
| quote: | | Apologies for the lack of scientific data to add to the discourse apart form my subjective impressions. |
Not accepted. This thread is not about sound at all. It's about discussing why there cannot be, isn't and never will be any audible difference between tube brands. The main topic movers happily confirm and prove to each other the abscence of audible differences and now you dare spoil the scientific purity with your anecdotal observations?! If you're not interested in discussing the fine points of watching paint dry you have nothing really to contribute here. |
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| DrewP |
| quote: | | Not accepted. This thread is not about sound at all. It's about discussing why there cannot be, isn't and never will be any audible difference between tube brands. |
Does that mean I can save heaps of money by having them prove to me that greencaps sound the same as teflon/tinfoil multicaps? Cool, think of all the cheap electros and bell wire I'll be able to buy to finish off my system.
In fact, if I stopped listening and just looked at published specs, audio would be so much cheaper.
Yay! I'm enlightened now!
Drew |
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| SY |
| Yes, magic is so much more fun than logic, reason, and evidence. ;) |
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| analog_sa |
| quote: | | magic is so much more fun than logic, reason, and evidence |
On the contrary. I found snippets like the one bellow better fun than any magic.
| quote: | | I've never heard a difference in "good" tubes working in the linear range. I have not listened very hard. |
I am still to meet an objectivist who is willing to listen 'hard'. This one at least honestly admits to listening laziness. |
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| SY |
| Most Objectivists are too busy reading Ayn Rand to spend any time messing with audio, so it's kind of a moot point. |
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| Colt45 |
| some of you guys really have to quit that crack habit, its starting to get to your heads. |
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| runeight |
:) :) :) :) So richly deserved!! What exactly was I trying to say? Who am I? And why am I here?
| quote: | | Not accepted. This thread is not about sound at all. It's about discussing why there cannot be, isn't and never will be any audible difference between tube brands. The main topic movers happily confirm and prove to each other the abscence of audible differences and now you dare spoil the scientific purity with your anecdotal observations?! If you're not interested in discussing the fine points of watching paint dry you have nothing really to contribute here. |
Since I started this thread, I must say that I don't feel this way. As I mentioned in another thread my background and, perhaps, temperment don't tend in this direction. In the late 19th and early 20th centuries the physicists believed that they had everything understood. All they had to do was to apply the theories that they had developed to the world that they knew.
Within the first decade of the 20th century Max Planck and Albert Einstein blew their self-satisfied universe apart with quantum theory and relativity. Both of these phenomena are totaly contrary the intuition and evidence of our senses. But they are very real.
In approaching the thread the way I did, I was trying to eliminate the things that I understand to try to get to the things that I don't understand about tubes.
| quote: | | How a pair of plates spaced apart with electrons wafting between them can exhibit an altered frequency response i cannot comprehend, all I can say is that they categorically do. |
I am not saying that this isn't true, only that I don't understand how it can be true. And if you all are hearing these differences, please help me to understand what is happening.
| quote: | | In fact, if I stopped listening and just looked at published specs, audio would be so much cheaper. |
Yes, I mostly agree with this. But I agree because I think that what are normally published as specs don't really contain enough data about how the equipment really works. For example, THD is a reasonable measure, but maybe not as relevant as IMD or Phase Distortion or even something else that we don't yet understand. But, what is it?
And it may be that an auditory experience is very subjective. It may be that for each individual any particular listening experience is different from other listening experiences and that this changes with our state of mind at any given time. I am willing to believe this, not as an "it's all in your mind" phenomena that is easily dismissed, but as a genuine part of the human cognitive system that makes listening to music a richer experience because of it.
But I do admit to trying to think about here whether we are talking about measurable differences among different brands of tubes or something else. And if something else, I really want to know what that is. Can you folks offer me some ideas? And I am not setting you up for ridicule (at least from my perspective). |
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| analog_sa |
Runeight
| quote: | | And it may be that an auditory experience is very subjective. It may be that for each individual any particular listening experience is different from other listening experiences and that this changes with our state of mind at any given time. |
At some level this undoubtfully is true, but there is little point going there. Most listeners seem to agree upon the effects of 'tweaks' so the experience is not so individual most of the time.
May i suggest a personal, first hand listening experience as an essential starting point for your journey. You only require a very simple audio chain to conduct meaningful tests and of course, certain listening abilities. If listening to the same track 50 times in a row proves too boring than maybe you're not too well suited for this position :) I have no idea what is your current audio setup but once you develop the ability to listen any setup is really good enough provided the signal path is short and simple.
I see very little point going through hundreds of simulations of simple (and well researched) PS topologies if you don't really listen to the effects each of these topologies have on the sound of an audio stage.
In fact the basis for the 'sound' of passive componets, wire, tubes, support structures, etc is well understood. The real issue with the 'objectivists' is not that a capacitor with a particular type of dielectric does not generate distortion or that group delay/skin effect in wire does not exist; their only real claim is that these effects are so low down that we can't hear them. And that is where the waters get really murky and no amount of simulation will tell you whether something is audible or not.
What makes things even worse for the scientist is that none of the classically recognised parameters like thd/imd have any meaningful correlation (outside of gross effects) to the listening experience. Years ago i noticed that the type of capacitor used in my phono pre had much stronger effect on the perceived tonality than the accuracy of the RIAA curve. And there were no Multicaps/Hovlands at the time so please don't tell me i was brainwashed by evil charlatans.
So, good luck in getting to the secret of audio nirvana, but with only theorising and simulating and no first hand experience the conclusions are very predictable. |
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| PRR |
> .02% THD is .02%THD, isn't it? Even if it's created by two different tubes?
Disagree on several levels.
0.02%THD in tubes is almost unknown. At high level, that needs a lot of feedback. At low levels, noise will mask any 0.02%THD. Yes, an analyzer may detect 0.02%THD on a small signal under 0.2% noise, and the ear may too. But I'd rather yack about more realistic levels.
Say you have one amp with "0.5%THD" that is mostly 2nd harmonic, and another that is "0.5%THD" but mostly 5th, 7th, 9th harmonics. The 0.5% 2nd is essentially inaudible. The 0.5% 5,7,9th subtly grates.
I feel that we should multiply each harmonic by its order. 0.5% times 2 is 1%. 0.5% times 9 for the 9th harmonic is 4.5%. The latter is 4 times more annoying than the former. That's not quite how the ear hears it. But it is a lot closer to how we hear than any THD number that sums all the partials the same. This was not an issue when THD was invented, because most amps had a declining distortion spectrum and the high partials "hid" behind the large 2nd and 3rd. When we got heavy feedback amps, we could make that 2nd and 3rd vanish, reduce the 5th, but in many cases the 7th and 9th are higher than in the simple amps of yesteryear.
THD is meaningless unless it is VERY small (20dB below noise at all levels), or the distortion spectrum is specified.
Why could "same" tubes sound different? Consider the grid wires. If they are equally spaced and pitched, the curvature is mostly "large" 3/2-power law, giving significant low-order distortion and insignificant high-order distortion. But now bend one of the grid wires a little closer. It will cause a steeper slope of the characteristic but will cutoff sooner. While passing through this range, the tube's smooth curve will kink. Much less than 1% compared to the total range of the tube. It looks the same on a curve tracer. You can't measure it on a needle-meter, and if you do you call it measurement error. It does not significantly affect the usual tube-type distortion tests done at 5%THD. But it puts high-order kinks and partials in the sound. This alone could explain some differences between mature tube factories with some high-spec products (US/EUR 1950s) and jury-rig tube factories with hungry unfussy customers (most current producers).
Note that tube specs are quite loose. 12AX7 is speced for just two conditions and no promise what it will do at any other condition. The spec-sheet condition is often in the top 50% of the tube's power ability, while we often run tubes below 25% of rated power. 6DJ8 is essentially speced for one condition, at much higher bias than usually used in audio (indeed so high that life is shortened). This means that a 6ES8 is "same as" 6DJ8... AT that one bias condition. The 6ES8 has several more spec points, but if you are selling "same as 6DJ8" you don't care about that. You can "meet spec" at the one or two spec points and be way off at other points.
I do have a hard time with conductors of different metals having different sounds. I'm more willing to accept that junctions of dis-similar metals have an effect, but there are so MANY junctions in any practical system that I don't know where to start. I will note that the press-in pins on vacuum tubes are very prone to poor oxide contact and small amounts of distortion. If you are going to tube-roll, at least use a good contact enhancer so you hear tube-guts, not fixable problems on pins and sockets. |
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| Sch3mat1c |
| quote: | Originally posted by DrewP
Folks, my experience of tube rolling is very limited but also very recent (within the last month).
[snip]
How a pair of plates spaced apart with electrons wafting between them can exhibit an altered frequency response i cannot comprehend, all I can say is that they categorically do. |
No, they don't. Chances are, differences in Gm, mu and Rp cause different levels of Miller C and other stage impedances, especially important if driving any sort of passive filter (as I mentioned above using 12AX7 vs. AT vs. AU in my preamp, which uses a passive Baxandall network).
Tim |
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| Sch3mat1c |
| quote: | Originally posted by analog_sa
The real issue with the 'objectivists' is not that a capacitor with a particular type of dielectric does not generate distortion or that group delay/skin effect in wire does not exist; their only real claim is that these effects are so low down that we can't hear them. And that is where the waters get really murky and no amount of simulation will tell you whether something is audible or not. |
Ah, so it's just like religion.. you can't prove that God doesn't exist so he must.
Tim (goes to church regularly in case you were wondering) |
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| analog_sa |
| quote: | | Ah, so it's just like religion.. you can't prove that God doesn't exist so he must. |
Not sure if i understand the above logic. I'd also be going to church regularly if God was speaking to me on a daily basis but what my ears can't hear does not necessarily exist :) |
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| SY |
| (doors open) "Fifth Floor; metaphysics, epistemology, ladies' hosiery, kitchenware. Going up!" |
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| Positron |
Just a thought run8, if you can purchase some insulated steel wire, you could make ICs and sonically compare them to copper/silver ICs. Although not a tube, it might be an interesting experiment.
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.02% isn't that hard to do in tube design, although I think you probably meant in an amp as a whole.
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Might want to read "Darwin's Black Box" by Dr. Behe. He is a microbiologist dealing with cells and systems in the body.
I believe his contention is that in the systems of the eye/sight, immune system, clotting system etc.; that the odds of putting together just one system is some -20 powers less than what scientists consider impossible, which I believe he said was something like 10 to the -25th or -45th powers. Since there are thousands of systems in the body, the odds of the body evolving is so close to impossibly even scientists would have to stretch their own definition immensely.
And each system has to be created whole, or else the system doesn't work (so why evolve it?) or the body dies (again how does it evolve if it dies?). Some systems would cause death before the body had a chance to replicate itself.
-----------------------------------
Another point, archeologists have dated some bible manuscripts well before the prophisied events, and in some cases even giving names of the future rulers and about the future kingdoms themselves.
Just something to ponder. |
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| smoking-amp |
One effect I have noticed from testing a tube circuit idea (on the bench) was the large variation of contact potential across tubes of even the same brand. (I was using diodes, so was easy to observe this on a curve tracer as a voltage offset.) This same affect in triodes etc. would lead to effective variations in the operating bias level and would no doubt cause differences in sound, since different portions of the tube characteristics would be used.
Another factor could be the variation of oxide coatings between tubes causing different levels of emissivity. And to top it off, emissivity changes noticeably during the first operating days of most tubes until it settles down to a stable value.
Tube rolling tests really need to include a bias adjustment for the tube being swapped. Also, I rarely hear of significant quantities of the same tube type being tested to see if the effects noticed are consistant. This is not to say that there couldn't be differences, just that I have my doubts of their repeatability in another amplifier which may be biased differently.
Don |
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| fdegrove |
Hi,
| quote: | | I will note that the press-in pins on vacuum tubes are very prone to poor oxide contact and small amounts of distortion. If you are going to tube-roll, at least use a good contact enhancer so you hear tube-guts, not fixable problems on pins and sockets. |
That's a very good idea. There's little point in spending big $ on rare tubes and than sticking them in lousy sockets.
| quote: | | I do have a hard time with conductors of different metals having different sounds. |
They do and it's not too hard to try it for oneself.
Cheers,;) |
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| smoking-amp |
| Just wanted to clarify that "contact potential" in my previous post is caused by dissimilar metal connections in tube construction and high temperature. (So as not to confuse this issue with the one about tube socket contacts, which is a different thing) |
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| Pjotr |
Hi,
Have 7 E88CC’s (with the gold clad pins) in my spare box. 2 are brand new and the other 5 are bought from a surplus store for almost nothing and have had various service life as can be seen from the various degrees of “blackening’ on the glass. All are from Philips and are looking optically the same. But measured Gm differs more than 30%. They also sound different. Although I must admit I have to listen carefully to hear a difference. Except one is sounding a bit dull and is probably near its life end. No doubt when I hook up a spectrum analyser the harmonic content will also differ slightly.
But what is it telling? Probably not much, only that those same looking tubes sound somewhat different and for sure will measure different. Oh what a surprise. When carefully measured (with a curve tracer) same tubes from different brands, no doubt you will find also different curves. Unfortunately I don’t have an automated curve tracer at hand to show you.
No magic, no religion, just engineering. Tubes are funny things.
Cheers ;) |
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| runeight |
| quote: | | Say you have one amp with "0.5%THD" that is mostly 2nd harmonic, and another that is "0.5%THD" but mostly 5th, 7th, 9th harmonics. The 0.5% 2nd is essentially inaudible. The 0.5% 5,7,9th subtly grates. |
Yes, my bad. The frequency spectrum of the harmonics is very important. And different curves will generate different harmonics. Does this happen for the same model tube? I guess the answer is, it depends on the specific type of tube and how critical the tolerances are to its operation.
| quote: | | Why could "same" tubes sound different? Consider the grid wires. If they are equally spaced and pitched, the curvature is mostly "large" 3/2-power law, giving significant low-order distortion and insignificant high-order distortion. But now bend one of the grid wires a little closer. It will cause a steeper slope of the characteristic but will cutoff sooner. While passing through this range, the tube's smooth curve will kink. Much less than 1% compared to the total range of the tube. It looks the same on a curve tracer. You can't measure it on a needle-meter, and if you do you call it measurement error. It does not significantly affect the usual tube-type distortion tests done at 5%THD. But it puts high-order kinks and partials in the sound. This alone could explain some differences between mature tube factories with some high-spec products (US/EUR 1950s) and jury-rig tube factories with hungry unfussy customers (most current producers). |
Yes, I believe this and other effects like it.
| quote: | | May i suggest a personal, first hand listening experience as an essential starting point for your journey. |
A very fair criticism. I actually do have some listening experience and I am working on some hardware that hopefully will enhance that. But, I haven't done the kinds of A/B comparisons where others are hearing differences from swapping out components.
| quote: | | The real issue with the 'objectivists' is not that a capacitor with a particular type of dielectric does not generate distortion or that group delay/skin effect in wire does not exist; their only real claim is that these effects are so low down that we can't hear them. |
Is that true 'objectivists'? Is the only claim that these effects are too small to hear?
| quote: | | So, good luck in getting to the secret of audio nirvana, but with only theorising and simulating and no first hand experience the conclusions are very predictable. |
Audio nirvana would be great. I'm not really trying to get there, I'm just trying to understand what this is all about. So far, there have been some very good answers. I can say, however, that often very good theory precedes the experiments that verify the effect. So, things are not always predictable. :)
| quote: | | Chances are, differences in Gm, mu and Rp cause different levels of Miller C and other stage impedances, especially important if driving any sort of passive filter (as I mentioned above using 12AX7 vs. AT vs. AU in my preamp, which uses a passive Baxandall network). |
Although it really doesn't make sense to swap these particular tubes, does it? Since the operating points, Zo, etc. will differ?
Skip, skip, skip . . . good stuff actually. But I think the moderators will kick me off the list if we go too far afield, even if it worthy of discussion.
| quote: | | Tube rolling tests really need to include a bias adjustment for the tube being swapped. Also, I rarely hear of significant quantities of the same tube type being tested to see if the effects noticed are consistant. This is not to say that there couldn't be differences, just that I have my doubts of their repeatability in another amplifier which may be biased differently. |
Hadn't though of that one. Surely someone has tried it.
Regarding contact potential, I am surprised that the contact potential variations are big enough to affect the tube's behavior. But, I guess it's true.
| quote: | | Oh what a surprise. When carefully measured (with a curve tracer) same tubes from different brands, no doubt you will find also different curves. |
But, if they have different curves, then they are different resistors to the circuit and they may sound different. My original thought was that if the curves are identical, the tubes must sound the same.
.| quote: | | I do have a hard time with conductors of different metals having different sounds. |
| quote: | | They do and it's not too hard to try it for oneself. |
I have a hard time with this too. How does it happen?
Thanks very much for everyone's replies. I have learned much |
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| salas |
I have rolled tubes in old Quad II amps. I have rolled tubes in old Mac amps. Same stuff like modern tube amps. The differences are audible and huge between tube makes. Every brand a general aural signature. Every type a more specific one.
Well it seems that in the 50s and 60s very few people had put such things under the aural microscope. In those days valves were a commodity. Remember how enthusiastically they have adopted the transistor? Bloody hell, they were living for years with excellent tube gear and they got tricked by crude solid state amps of the time! Same with CD. Remember? In the start they said all players are sounding the same and that are inherently perfect...ha! ha! ha!
I just believe that audiophilia just now is getting digested as a culture that done its first cycle. We are wiser as a hobby society now. Most of all we can communicate through forums. Imagine if Peter Walker could air his views to the people like Nelson Pass does today....
And another thing..its amazing how such obvious things that we listen to are masked by our mental prejudice... In a psychoacoustic seminar I have been told that hearing is the most complex and elusive sense because 80% of it is processed by the brain.... Just imagine....What G.Bush would prefer for his audio gear and what...Noam Chomsky! |
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| fdegrove |
Hi,
| quote: | | My original thought was that if the curves are identical, the tubes must sound the same. |
That is quite true really.
To understand why tube rolling is so popular amongst die hard audiophiles you have to know tube history, economic history on a continent to continent basis.
Brand reputation is a major factor too and sometimes,with some particular tube types, not so well reputed brands can surprise you.
As an example:
In Europe it was not uncommon for instance that RFT East-Germany would manufacture some tube types for Telefunken ( diamond cast logo included).
Those EF86s weren't bad but the homemade TFKs were better still...
The ECC range from RFT is often a load of **** and it WILL show on the curve tracer too.
How many people don't think Tungsram is a Eastern-European brand and therefore think those tubes are inferior?
Well it isn't and alot of their tubes are absolutely great.
Let's not forget either that those tubes we're handmade and that some manufacturers concentrated precision on particular parameters that could be more relaxed with others and vice versa.
Having a variable bias will help to some extent, surely. In reality people don't have variable bias and go by their ears.
I never had good curves from a bad sounding tube but had often very good sound from a well tracing tube, so, to my mind there must be a correlation.
Certainly, materials used, cnstruction methods and measures against susceptability to microphony all add to good quality.
The worst and oddest sounds I ever heard were from the early Chinese tubes...phasey imagery with all the musical emphasis in the wrong places.
Absolutely weird, almost as if a recording engineer had the whole thing panned the wrong way around.
Did they measure like ****? Yes, sir!
So much so that you could just as well have invented new names for them; 12AX7S(hit) for example.
Enough ranting for the day/
Cheers,;) |
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| PRR |
> My original thought was that if the curves are identical, the tubes must sound the same.
If you mean: the curve plotted with exact (or at least semi-quantum) precision, that may be most of the sound.
Practical curve tracers are 1% accurate at best. Actually when you slap a tube to its limits, as often done in tracers, you run into hysteresis and other effects that cause the trace to be different going up than going down. Tracers are handy for quick checks, and to estimate max power and approx THD near that power.
The ear is sensitive to errors smaller than 1%, smaller than most tracers try to measure. We could propose a "close-up" tracer that would (say) sweep the grid from 1.000 to 1.010 volts and measure current-change with similar accuracy. This type of test would show kinked-grid and cathode hot-spot small nonlinearities, which may be what people are hearing. However I suspect it would be simpler to drop the tube in a basic amplifier and do tests (instrument and listening) than to fancy-up a curve tracer.
Vacuum Tube Valley magazine does a lot of "Tube Shoot-Outs", comparing different brands and years of the same tube. They often do both curve-trace tests and listening tests. The gross measurements do show differences between "same type" tubes, sometimes 10:1 difference between NOS TungSol and New-China in THD at reasonable levels. (I wish they would show the spectrum.) In the listening test, they do sometimes re-bias each tube (though it may be the same bias for all tubes, rather than an "optimum" bias for the specific tube in the socket).
And just to be a grump:
> they were living for years with excellent tube gear and they got tricked by crude solid state amps
No, we mostly had crappy tube stuff. Yes, there were the Quads and the Macs, and a few Eicos that didn't suck too bad (volume pots always scratched, and tin jacks never got good connection). Bogen made (probably by mistake) a pretty decent 150W tube PA amplifier; a trio of these earned me pizza-money for several years, because it did sound better (and take abuse more gracefully) than many of the transistor amps of the day.
But there was a lot of pretty-bad and some really awful tube gear. I had two low-power (2 watt) stereo amps, one a pair of 60FX5 and one with five transistors per channel. While the sand amp rasped a bit at soft level, it gave much flatter response and better speaker damping than the no-feedback pentode. (Remember: from 1935 to 1985 no commercial design and essentially no hobbyist designs used power triodes.) I had some very early and very inoffensive HH Scott transistor amps in service until recently.
Most tube gear sucked, more or less. The stuff that has survived isn't typical: we trash-binned a lot of it. |
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| analog_sa |
| quote: | | Remember: from 1935 to 1985 no commercial design and essentially no hobbyist designs used power triodes |
Isn't this a bit of a strong statement? I happen to posess a GEC 14W PX25 interstage PP which seems to be late forties vintage and no doubt others also exist. |
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| Sch3mat1c |
| quote: | Originally posted by runeight
Although it really doesn't make sense to swap these particular tubes, does it? Since the operating points, Zo, etc. will differ?
|
It does to me. The circuit was designed for AU, but that doesn't have enough gain; AX has enough but too high a Zo distorts the frequency response and doesn't sound good. AT just happens to have a nice low Rp. By a happy coincidence, if I were to calculate good operating points for each of the tubes, the bias resistors would come out about the same, so bias is not an issue.
| quote: | Re: sound of metal
I have a hard time with this too. How does it happen? |
Guess I'll have to go unspool some of that stainless steel lockwire and run my speakers off it for a few days... ;)
That reminds me, I was going to build an amp using resistive wire such as that some day. Too bad it tins like ****.
Tim |
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| runeight |
Well, let's see . . .
| quote: | | And another thing..its amazing how such obvious things that we listen to are masked by our mental prejudice... In a psychoacoustic seminar I have been told that hearing is the most complex and elusive sense because 80% of it is processed by the brain.... |
I don't think there is any question about this. Everyone should know that often what he/she hears is whatever he/she is willing to process.
| quote: | | Did they measure like ****? Yes, sir! |
Which is at least part of what I'm trying to pin down, that bad tubes are also measurably bad.
| quote: | | Vacuum Tube Valley magazine does a lot of "Tube Shoot-Outs", comparing different brands and years of the same tube. They often do both curve-trace tests and listening tests. The gross measurements do show differences between "same type" tubes, sometimes 10:1 difference between NOS TungSol and New-China in THD at reasonable levels. (I wish they would show the spectrum.) In the listening test, they do sometimes re-bias each tube (though it may be the same bias for all tubes, rather than an "optimum" bias for the specific tube in the socket). |
All makes sense to me. I truly do believe that tubes with the same label (and not re-labelled) have a wide variation and can sound different for all of these reasons.
| quote: | | By a happy coincidence, if I were to calculate good operating points for each of the tubes, the bias resistors would come out about the same, so bias is not an issue. |
I know you're right on this one.
| quote: | | Guess I'll have to go unspool some of that stainless steel lockwire and run my speakers off it for a few days... |
Oh no, I believe this because you're talking about fairly long lengths where the properties of stainless will matter. It is hard for me to see, though, that this will matter much for very short lengths. For example, I don't recall what the connecting strips in tubes are made of, but whatever they are they have to be resistive because they are spot welded. Yet, I don't think we talk about the resistance of these wires as having an impact (at least in audio) because they probably don't.
| quote: | | Wonder where matter and energy came from? What happened before the big bang? |
Well, now I never thought we'd get here, but it is relevant. Actually, about 10e-39 seconds after the ignition of the big bang, the universe was approximately a sphere about the size of a nickel. Now, you can't think of this as a small ball of matter inside a very large empty space that got filled up. Everything we know as time and space was actually inside the ball. So, what was outside of it or before it? No matter what the answer is, tuberolling is a direct consequence of the big bang or whatever surrounded it and preceded it. :)
Furthermore, as I understand the current inflation theory (and I am definitely rusty) the universe sprang from absolutely nothing. Not only that, if you add up all of the matter in the universe and all of the gravity (which amounts more or less to negative matter) it all still adds up to . . . zero, nada, nothing.
So, folks, when you make posts to this forum and your juices get going about someone's stupid post, remember that you are basically . . . . . . nothing. :scratch2:
Thanks for being so generous with your time and comments. |
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| smoking-amp |
Sorry, I couldn't resist! Its not that we are all nothing, the big kabosh produced equal amounts of somethings and anti-somethings. Thats why we are always having all these arguments. Only when one considers all points of view even handedly does one end up with truly nothing!
Maybe we should start concentrating our energies on how to make a time machine, then we can all go back and buy up those rare tubes we all want. :D
regards,
Don |
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| dhaen |
| quote: | Maybe we should start concentrating our energies on how to make a time machine, then we can all go back and buy up those rare tubes we all want.
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Valves could then go missing - mid song - from peoples equipment :cannotbe: |
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| Positron |
"Furthermore, as I understand the current inflation theory (and I am definitely rusty) the universe sprang from absolutely nothing. Not only that, if you add up all of the matter in the universe and all of the gravity (which amounts more or less to negative matter) it all still adds up to . . . zero, nada, nothing.
So, folks, when you make posts to this forum and your juices get going about someone's stupid post, remember that you are basically . . . . . . nothing.
Thanks for being so generous with your time and comments."
So who made matter and ant-imatter? By what laws, and all the universe is governed by laws of some sort, did "nothing" become something? Or did laws just come into being by themselves?
"Nothing" becoming matter and anti-matter is a little far fetched to me, and only a guess anyway. I believe Einstein definitely believed in a supreme being. |
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| smoking-amp |
"Valves could then go missing - mid song - from peoples equipment"
We just take the old tubes back and swap them when were done with them, no one will notice. Thats why tubes are always burning out, Time Bandits, they know whats worth stealing!
"By what laws, and all the universe is governed by laws of some sort, did "nothing" become something? Or did laws just come into being by themselves?"
You have a point here, its truly Spooky how mathematics seems to work so well. Especially considering where present math/physics is leading. As far as the do unto others thing goes, I always liked the Chinese proverb about the man who wakes up and can't decide whether he has awoken from a dream or is currently dreaming. Ever wonder why everyone has to sleep regularly? What if we all just wake up as someone different every day, but with the monotonous memories of always being that person. Puts a new light on being sympathetic to others, you might be having an argument with yourself if you aren't careful about thread posting times on the net!
Guess we should apologize for threadjacking runeight's thread, but maybe he's still sleeping! |
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| runeight |
| That's right, you're in the Matrix right now! :clown: |
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| Positron |
Very true.
It seems that over time, again and again I have come up missing parts, tubes etc. Could it really be...... |
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| stormy |
I got a totaly diffrent picture from this post about tube rolling.
(or am i just paranoid)
Tuberolling:buying cheap valves ,removing printing and "rolling"
cheap valve over a screenprint making it a exspencive vale
eg (mullard)
cheap valve £2.00
Mullard NOS sold on Ebay £35-XXX depending on valve.
If i am wrong about this please forgive me, but I do know
it goes on so beware.
stormy |
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| runeight |
I hadn't thought about that!!! You may be exactly right!!
But, most of the time today, the term simply means changing out tubes for another set to find "sonic" differences. |
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| thoriated |
| quote: | | Since I have come back to vacuum tube audio in the last several years, I am fascinated by the concept of tube rolling. I have heard both sides of this issue expressed. Maybe some of you guys can give my your further opinions on this subject. |
Of course tube rolling is 'real' and has significant effects on equipments' sound in many cases, just as different types of capacitors, resistors, transformers and variations in circuit topology affect sound.
I still recall when I built my phono preamp, merely dialing up the supply voltage from 325VDC to 375VDC made a perceptible improvement in the sound at the line level output. Same components and everything - just a slightly different bias and a minor change in harmonic distortion spectrum, I imagine. |
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| Positron |
| And cryo-ing a tube also makes a difference, a better sound. |
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| ashok |
| quote: | | just a slightly different bias and a minor change in harmonic distortion spectrum, I imagine. |
You should use some Spice program like Beige Bag which is very easy to use.
You can see very easily how the distortion levels and the spectrum change with changes in the operating point . In spite of the speed of the computer it still takes time to try out all the combinations you want.
IMHO the spectrum that drops with increasing frequency probably sounds better than lower distortion with odd order harmonics coming up higher than even order harmonics. I think the sound will be harder if the higher order harmonics do not drop rapidly .
And with all simulations they are just indications of circuit performance, as the models are never perfect. So you will eventually have to build your final circuit to see if it really is the best.
Cheers. |
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| ashok |
Tube rolling , or plugging a different tube into the socket to see how it sounds , is IMHO not really a good way to test tubes.
I think that tubes of a type , say 12AX7 , from different manufacturers are not exactly the same. They belong to the generic same type by the few parameters that we usually mention. That really does not make them exactly the same.
Like the NE5532 debate in another thread. Those from Signetics sound different from those from TI.
So we should have 12AX7 , 12AX-7a , 12AX-7b etc. They are not all the same. So if some type sounds better in the circuit it could be at its best operating point. Maybe if the other passive parts are changed the competing tube might also sound as good if it is at IT's best operating point.
So the comparison 'may' not be correct. So tube rolling can give interesting results but not necessarily conclusive ones. |
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