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Old 21st October 2007, 05:25 PM   #1
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Quote:
Originally posted by Eli Duttman
The 12AU7 ... is not particularly linear. The 6SN7, 6FQ7/6CG7, and 12BH7 are (IMO) better choices.
The 12AU7/5963/6189s can make stellar audio components. If you cannot get one to be linear over a 1-2V audio signal -- you can't design tube kit at all.

This isn't targeted at any one person, it's just sad to see some tubes get bashed, when it's nothing more than repeating something someone else posted on a page that isn't even correct. This regurgitation of misinformation shouldn't happen. There aren't 10 holy grail audio tubes (300b, 2A3, 807, el34, kt88, 12ax7, 6922, 6sn7, 6l6, 6sl7) and everything else is garbage. It just doesn't work that way. There were literally thousands of tube types made and many, many many of those can make great audio amps -- including the 12au7. I would much rather use it than a 12ax7 and you see those in everything... and everyone thinking its a great audio tube... of which i don't. Not to mention.. i do believe the 12au7 was meant to capture some of the 6sn7's market -- and everyone thinks that tube is great... alas...
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Old 21st October 2007, 06:12 PM   #2
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Quote:
Originally posted by Cycline3


The 12AU7/5963/6189s can make stellar audio components. If you cannot get one to be linear over a 1-2V audio signal -- you can't design tube kit at all.

This isn't targeted at any one person, it's just sad to see some tubes get bashed, when it's nothing more than repeating something someone else posted on a page that isn't even correct. This regurgitation of misinformation shouldn't happen. There aren't 10 holy grail audio tubes (300b, 2A3, 807, el34, kt88, 12ax7, 6922, 6sn7, 6l6, 6sl7) and everything else is garbage. It just doesn't work that way. There were literally thousands of tube types made and many, many many of those can make great audio amps -- including the 12au7. I would much rather use it than a 12ax7 and you see those in everything... and everyone thinking its a great audio tube... of which i don't. Not to mention.. i do believe the 12au7 was meant to capture some of the 6sn7's market -- and everyone thinks that tube is great... alas...

The 12AU7 is OK as a cathode follower and as a "concertina" phase splitter. It's mediocre linearity makes it (IMO) a poor choice as a voltage amplifier. The 50% smaller heater draw and identical mu, compared to the 'SN7, makes the 'U7 attractive to a designer, but the plate curves don't lie.

I AGREE that all sorts of tubes can be used to get GOOD audio results. For starters, add the 6V6, 7591, EF86, 5687, 5965, and 12AY7 to that list. Obviously, there are many, many, more.
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Old 21st October 2007, 11:28 PM   #3
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Quote:
Originally posted by Eli Duttman
The 12AU7 is OK as a cathode follower and as a "concertina" phase splitter. It's mediocre linearity makes it (IMO) a poor choice as a voltage amplifier. The 50% smaller heater draw and identical mu, compared to the 'SN7, makes the 'U7 attractive to a designer, but the plate curves don't lie.
This is EXACTLY the nonsense I'm talking about. We are addressing a few volts AC max... at all sections of the amp except the driver and the outputs and you are saying it's not linear. Let me make myself clear - IF YOU CANNOT GET THAT TUBE LINEAR IN A PREAMP YOU CANNOT DESIGN TUBE GEAR. It's that simple. Given that it's not as linear as some... you are talking about a couple volts vs. the ability to swing three digits worth of voltage. The tube curves are over 0 to 300 volts or more... who cares if it's not as linear as another tube... it's straight where you should choose to bias it.. and a 2V AC signal isn't going to change that AT ALL. Further, the listening tests actually bear out that it is a very nice sounding tube as well. The tube curve isnt everything. I have tubes that test identical on my tube tester and in circuit that DO NOT sound the same. Again.. this is nonsense... and I refuse to let these stereotypical analogies of one is better than another persist...
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Old 22nd October 2007, 12:27 AM   #4
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Originally posted by Cycline3


This is EXACTLY the nonsense I'm talking about. We are addressing a few volts AC max... at all sections of the amp except the driver and the outputs and you are saying it's not linear. Let me make myself clear - IF YOU CANNOT GET THAT TUBE LINEAR IN A PREAMP YOU CANNOT DESIGN TUBE GEAR. It's that simple. Given that it's not as linear as some... you are talking about a couple volts vs. the ability to swing three digits worth of voltage. The tube curves are over 0 to 300 volts or more... who cares if it's not as linear as another tube... it's straight where you should choose to bias it.. and a 2V AC signal isn't going to change that AT ALL. Further, the listening tests actually bear out that it is a very nice sounding tube as well. The tube curve isnt everything. I have tubes that test identical on my tube tester and in circuit that DO NOT sound the same. Again.. this is nonsense... and I refuse to let these stereotypical analogies of one is better than another persist...

My OPINION of the 12AU7 is not particularly favorable. I think it's blah, not bad. Opinions, including mine, do not equate to absolute fact. FWIW, my view is commonly held. If you like the tube, by all means use it. After all, only your ears matter in your listening room.

Please stop issuing insults. I have not insulted you. Honest differences of opinion are why horse races are conducted.
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Old 22nd October 2007, 12:49 AM   #5
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Nonsense. This is a TUBE that can handle hundreds of volts... you are talking about 2 VOLTS. It is NOT OPINION when it comes to that tube being LINEAR OVER A 2 VOLT RANGE. Absolutely 100% undeniable FACT that it is NOT an opinion. END OF STORY. If you take that as an insult... then it's simply because you are inferring it.. and I assume still claiming that the tube can't be linear over a 2V AC range. Which as I said before is non sense. I also said, none of this was directed at any one person.. but the stereotypical... this tube is bad... should play out... and it should.
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Old 22nd October 2007, 01:15 AM   #6
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I don't agree and my measurements with 12AU7's CCS loaded with a small output swing were still bettered in THD by a number of others, most notably the 6SN7. All tubes were NOS.
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Old 22nd October 2007, 03:23 AM   #7
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Let's look at the curves in question.... as for your measurements... you are 1 person with a few tubes... which is not representative of a whole as well as if we went on sheer measurements alone... we'd be solid state guys and single ended tube audio would not exist. And Im sure there are plenty of gear guys and gals here that would gladly tell you their high THD SE amps stomp the (fill in your favorite expression) out of typical hi fi stuff with great numbers.

Click the image to open in full size.
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Old 22nd October 2007, 04:43 AM   #8
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Quote:
Originally posted by Cycline3
Let's look at the curves in question....
Curves are generally representative of the model, but not exact for the individual device under test.
Quote:
Originally posted by Cycline3
as for your measurements... you are 1 person with a few tubes...
This is true. However what I did was basically the same as Morgan Jones did in his book, so I don't see how it's irrelevant. Besides, I'll take my measurements over your trying to prove linearity by looking at a set of curves that are so far out of scale for what you're trying to see
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Originally posted by Cycline3
which is not representative of a whole
Who ever said it was? But they are representative of my tubes in my test rig. They are quality samples of good brands. I can't be bothered to get my notebooks out of the workshop to give the exact details.
Quote:
Originally posted by Cycline3
as well as if we went on sheer measurements alone... we'd be solid state guys and single ended tube audio would not exist. And Im sure there are plenty of gear guys and gals here that would gladly tell you their high THD SE amps stomp the (fill in your favorite expression) out of typical hi fi stuff with great numbers
This is funny. Because you're all defensive about the 12AU7, which should only be used in MI amps in my opinion, measurements are useless? There are many ways to measure things and of most interest to me is the spectrum, as well as the levels. I don't do single bit THD measurements except as a quick check for faults.

I have no aversion to SS and tubes are not a religious experience for me. I use whatever works best for what I'm trying to achieve.
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Old 22nd October 2007, 11:26 PM   #9
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Quote:
Originally posted by Brett
Curves are generally representative of the model, but not exact for the individual device under test.... I use whatever works best for what I'm trying to achieve.
More nonsense from more nonsense. Why can't you just admit your wrong? I don't know of ANY tube that doesn't have a 2v linear section to the tube curve... zero... regardless of construction or intended use. Saying that a 12au7 is only suitable for a musical instrument amplifier is only illustrative of one thing... complete ignorance of the tube/subject we are talking about!

As far as getting back to the subject, we should do that... but it does point out something FAR more important to the newbie here.. .that many people will spew stupid audio stereotypes without *any* basis in reality because someone somewhere read it and mentioned it at the audio club meeting a year or so ago...or whatever the unproven source....... so *tired* and so utterly lame.
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Old 23rd October 2007, 02:21 AM   #10
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Quote:
Originally posted by Cycline3


More nonsense from more nonsense. Why can't you just admit your wrong? I don't know of ANY tube that doesn't have a 2v linear section to the tube curve... zero... regardless of construction or intended use. Saying that a 12au7 is only suitable for a musical instrument amplifier is only illustrative of one thing... complete ignorance of the tube/subject we are talking about!
Now you're getting nonsensical. I posted that I had made actual measurements from tube samples and you wish to dispute that based upona highly enlarged scan of a print of a page that represents a tube type. Incredible. I have a degree in electronics and a couple of decades experience working in the field. I find the 12AU7 to find it's best appliction in MI gear. I strongly prefer other types in reproductive electronic systems. If you don't like that I couldn't care less. It consistently MEASURES worse, and therefore a generalised set of curves and what they might mean to you is irrelevant to me compared to the actuality of an in circuit test.
Quote:
Originally posted by Cycline3
As far as getting back to the subject, we should do that... but it does point out something FAR more important to the newbie here.. .that many people will spew stupid audio stereotypes without *any* basis in reality because someone somewhere read it and mentioned it at the audio club meeting a year or so ago...or whatever the unproven source....... so *tired* and so utterly lame.
I stated I made measurements myself, similar in format to Morgan Jones in VA, and that's hearsay from a club meeting? Incredible. You're making a strawman as your argument has no merit based upon what you've posted.
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