An analytical look into the sound of various tubes

[c_dk]

To keep from sidetracking a previous thread I have opened this one.

I have read many poetic descriptions of the sound of various tubes. It interests me in how these various tubes must interact with the tube circuits to cause some tubes to be pleasing and some not so much.

Does anyone know of a study of how these tubes response, most likely frequency distribution, causes such positive and negative reactions?

It was pointed out that some expensive vintage tubes might be revered because of their scarcity not necessarily because of their positive sound characteristics.

I am also sure that there are many bottles of rare vintage wine that now contain vinegar....until you open one how do you know?

It is easy to make a sound pleasurable to a individual.....just push the right frequency distribution buttons to please a individual and you can make something sound good to them, but maybe not to someone else.

Creating a stereo image is more complicated but still has to be a interaction of those two audio streams we call L and R.

Has anyone made even a simple basic comparison of the frequency and noise characteristic of various tubes?

I have a mostly stock 3x sitting around that has been loaned out a number of times to locals and pronounced as sounding great. With such a simple few tube circuit, I would think it should make a decent 12x test mule.

 

[arts]

As there has never been any correlation whatsoever between subjective and qualitative analysis,I can't see this exercise as having any value whatsoever.
Other than to promote more arguments and divisivness between members,this will have all the value of another cable debate.In before the lock

 

[BillWojo]

I have a complete tube pull from a Dynaco ST-70 amp. Found them at a yard sale for cheap. The Mullard power tubes tested strong. EL34 I believe, to lazy to dig them out at the moment. Anyway, every SE amp that they will fit into sounds so much better than any of the newer tubes I have tried. It's consistent, no matter what's in the SE amp, these are always a nice improvement.
I also have a set of GL KT66, not the reissues, that a friend gave me. They test on the low side but have killer sound. i DO understand why folks pay the prices that they do for some of these legendary tubes. I just would never run them in an amp that is hard on tubes.
They sit in a box and I bring them out when I want to see what an amp is really capable of. Yes, there is magic in those glass bottles.

BillWojo

 

[gadget73]

A lot of this is circuit dependent too. The more feedback you have, the less difference any given tube is going to make provided its a good tube that measures within normal parameters for that tube type.

 

[manu et deo]

Oh to quantify subjectiveness. My wife has not eaten meat in 28 years. Yet she continues to tell me when it smells good or not. I feel audio is the same way. YMMV

 

[c_dk]

There should be no reason for any argument or divisiveness, people hear differently......it has been given for years that the reference standard is 3dB for most frequency linearity.......40 + years of client interaction has caused me to wonder if that means anything at all......I have had clients that could perceive 1 dB, others that well be best left unsaid.

Again anything already out there........frequency response? square wave response?

 

[kward]

There are a few random things available that I'm aware of. In his book Valve Amplifiers, 3rd Edition, page 189, Morgan Jones measures some small signal tubes with mu of about 20, for harmonic distortion under controlled testing conditions. He tested 18 different types of small signal triodes under these controlled conditions. In summary he found that the 6SN7 was generally the lowest distortion producing tube while the 12AU7 was the highest distortion producing tube.

Measurements don't tell the whole story though, as I think it has some to do with the circuit and how much feedback is applied also. Feedback especially tends to minimize differences.

If you want the specifics of his testing, I will point you to the purchase of his book so you can read for yourself.

 

[luvvinvinyl]

Too many uncontrolled variables, to create a reliable data set with global predictability.

A given tube will perform differently in different circuits. Now, take a given tube and amplifier, from one set of speakers to another, and the owner may well prefer one set over another. Now, move the tube, amp, and speakers from one room to another, and the sound is different again. Now, introduce another listener, and the preferences may be the same, or they may flip.

Each person's preferences are best discovered experientially. (Listen for yourself.)

 

[s-petersen]

Dave Gillespie has some done testing on various tubes for power, and maybe distortion, but I am not sure about noise and sound. There was a tube vendor selling 6SN7's I think that was testing for sound and noise, using a headphone amp.
I would think the linearity, and operating point of a particular tube (or brand) would have some impact on the sound, and possibly leakage would have an impact on noise.

 

[sKiZo]

If this thread is about quality of sound, in my book, it's more or less as stated, dependent on the end user's tastes. That said, I've some relatively inexpensive tubes that run rings around some of the "best" ...

Luck of the draw really.

And speaking of 6SN7's, anybody ever hear of Greylock? Got one here that's my go to tube for the center driver on my amp. Looks suspiciously like a Sylvania "bad boy" it replaced at maybe a tenth the cost, and runs rings around it for SQ.

Next favorite is a much maligned RCA "coin base", so maybe I just got a tin ear, eh. ;-}

PS ... lot depends on interaction with other tubes as well. That's the fun part of rolling - mixing and matching any and all combinations of whatever you've got in the box until you have one of those "aha!" moments. Doesn't even have to be in the same equipment - I've a tube buffer, and changing one tube in that can completely change the character of the main amp's sound.

 

[s-petersen]

We used to have a Greylock electronics store in Middletown NY it closed in the early 90's I think. They sold Sylvainia / ECG stuff mostly

 

[primosounds]

To keep from sidetracking a previous thread I have opened this one.

I have read many poetic descriptions of the sound of various tubes. It interests me in how these various tubes must interact with the tube circuits to cause some tubes to be pleasing and some not so much.

Does anyone know of a study of how these tubes response, most likely frequency distribution, causes such positive and negative reactions?

It was pointed out that some expensive vintage tubes might be revered because of their scarcity not necessarily because of their positive sound characteristics.
.

Overly verbose descriptions of a tube's sound is always suspect. There are too many variables to make the sonic qualities of a particular transferrable to another persons audio system.
Vacuum Tube Valley magazine put out a rating system of various common audio tubes which they called "tube shoot outs". All of the mags are available online for your perusal.
If you are creative there are a lot of variations, that is different heater voltages, or different pin outs of expensive tubes that in a different iteration can be quite affordable.
What one really learns after building your own equipment is that it is not the tubes that have the greatest contribution but the circuit and most importantly the heart of the circuit, the power supply.

 

[sKiZo]

I was gonna do a parody of an Absolute Sound audio review, but the actual material is bizarre enough as is ...

 

[Tom Bombadil]

Next favorite is a much maligned RCA "coin base", so maybe I just got a tin ear, eh. ;-}
.

This is one of the classic "beauty is in the eye (ear?) of the beholder" tubes.

I've read a lot of opinions on the RCA coin-base 6SN7. I'd say about 80% of them were very negative. To the point of considering them to be junk. But then there are a few who think it is marvelous. I know two people who have at least a dozen of them and consider them to be their all-time favorite 6SN7.

 

[Nixxuz]

The only correlation I've been able to figure out is that everything that's from the mid 1950's is better than anything made now IF, it's hard to find and therefore expensive.

Which I think is a load of horsepoop, but that's completely my opinion.

I know generic Chinese tubes that have shooting stars on them are terrible. Haven't found anyone who disagrees with that yet.

 

[c_dk]

Two well known transducers are accepted as having their performance affected by their interaction with outside factors......phono cartridges and their corresponding turntable and speakers and their room and placement there in.

The community over the decades have found ways to measure the above interactions and those measurements can give insight as to why say a certain speaker will sound great in one room but bad in another.

Yes on top of that the performance of said speaker could be reversed to two different listners but we can measure and gain insight into why it sounds different in each space to each listener.

So going back to my orginal proposition......what measurable changes might two different tubes have in a circuit to cause a positive or negative perception of these tubes.

I personally believe that the linearity of the frequency response must be a large factor when you think through the whole method of creating a stereo image. Any phase changes imparted should have additional effects due to the altering of the psychoacoustic event we experience while listening.

While distortion characteristics have been mentioned, most audio listeners tolerance of higher levels or distortion would cause me to think this is a lesser factor for audio.....I do believe the guitar tube universe though is completely different.

I did run a square wave through the PAS3x to find the true null of the tone controls and did capture those images on my laptop scope......trying to photograph my Techtronics scope with my phone camera is too hit or miss.

 

[sKiZo]

This is one of the classic "beauty is in the eye (ear?) of the beholder" tubes.

I've read a lot of opinions on the RCA coin-base 6SN7. I'd say about 80% of them were very negative. To the point of considering them to be junk. But then there are a few who think it is marvelous. I know two people who have at least a dozen of them and consider them to be their all-time favorite 6SN7.

This one's adapted to replace a 12AU7. Raises another point - the circuit is a compromise that can handle a wide variety of tubes without mods. Optimizing for a specific type would certainly make a difference, and I'll leave it to the gurus with the calculators to decide whether that's a good thing or a bad thing ... ;-}

 

[4-2-7]

Too many uncontrolled variables, to create a reliable data set with global predictability.

A given tube will perform differently in different circuits. Now, take a given tube and amplifier, from one set of speakers to another, and the owner may well prefer one set over another. Now, move the tube, amp, and speakers from one room to another, and the sound is different again. Now, introduce another listener, and the preferences may be the same, or they may flip.

Each person's preferences are best discovered experientially. (Listen for yourself.)

This here is the truth in really all to do with audio. Pretty much why I don't recommend anything when asked about what SQ is better. I'll add one more here Ernie, acclimating over time, our mood changes day to day and week to week. Any judgement should be done over time and different moods and music.

 

[trainbuftony]

Vacuum tube valley did some of this type of thing. They tested various preamp tubes on an amp which they built for the purposes of testing them. You may or may not be able to draw any valid conclusions from their reporting. The last time I tried I was able to download the entire set of magazines for free, which is some good reading... My opinion having worked on this stuff: most hi fi circuits have feedback around them and will always tend to mask differences between tubes of the same type. Failed tubes, (gassy, shorted,weak unmatched) tubes may sound bad because they exceeded the ability of the feedback to correct small errors. Good tubes will sound nearly exactly the same in a propperly working stage with feedback. The subtle nuances between tubes in one amp, my or may not translate to simmilar differences in another amp... One point that vacuum tube valley made in their article is that doing this type of testing with any meaningful sample size is extremely expensive!

 

[tubeactive]

Oh, Yes...trying tubes can be quite expensive...we do have to pay to play...

Quantifying specific tube amp circuitry with resulting tube sonics, distortion spectrum plotting or noise floor analyses can be quite time consuming; even boring. Test equipment can be quite expensive, while the industry's chosen specifications can quickly be seen as "inadequate" in describing sound quality. It is the "sound" which is most important to us. Have any of you taken any test equipment with you to any of the audio salons, during a critical listening session to choose components ? I didn't think so...We rely on our ears. But, our ears are so subjectively different from one another. Each of our psycho-acoustical, brain to ear mechanisms is unique.

Yet, through all of our physiological and psychological differences, plus our preconceived notions and expectations, we each know what certain acoustical instruments sound like...or at least we each think we know what certain instruments should sound like...Right now, I think I might be both confused and probably confusing...LOL...

There is a certainty, however, while tube rolling with a specific amplifying device, when we each know which tube we prefer. If not, then a system "resolution" deficiency exists. We cannot blame any uncertainty on the level or type of feedback. Every user of any feedback equipped amp or preamp knows which tubes they prefer, regardless of the type or amount of feedback within the circuit topology. Rolling tubes is much easier than rolling transformers and I can assure all of us that if you change an input, interstage or output tranny, you will prefer one tranny model over another. Users of active, feedback equalization equipped phono preamps or line stages will surely "know" which tubes they prefer...

So, yes, we each have to pay to play, in order to find our "choices" in circuitry, tubes and trannies...A very satisfying result can occur when you have your favorite preamp or amplifier design tested objectively by an engineer, or another engineer with more authority. Once objectively tested and quantified, adhering to high quality specification standards, thus approved, then you can really get down to enjoying the sound of that amplifying device.

Using "tried and true" circuits only goes so far. You can love the sound, but gaining knowledge that your amp or preamp circuitry actually "tests well" can confirm your affection. Of course, your brain to ear, psycho-acoustical nature will still prefer certain tubes...