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In Reply to: RE: To worry about which variety of 12AU7 is better, seems a bit pointless to me posted by Timbo in Oz on July 10, 2015 at 00:37:32
I see you're quite definite re the 12AU7. I don't understand why so many amps are designed to use that tube, if they are so bad. Generally speaking the 12AT7 is easier to find in good shape and are less expensive than equivalent 12AU7s. I bought a little headphone amp, a Bravo 2 which uses `1 tube and it is a 12AU7. I found that rolling it had less of an impact on the sound than I usually find. I am not sure why this is but I suspect the SS element of the amp is it's output stage, which overwhelms the input stage signal. I like the amp, any way, but use my larger desktop with 6080s more than the Bravo. I haven't tried anything other than 12AU7s (ECC82s etc..) in it.
Steve
Follow Ups:
Because no 12AU7 made actually sounds good as a gain tube?Maybe?
And, likely you are you're own man, when it comes to audio. Good for you.
:-)
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
Edits: 07/10/15
I have a great deal of respect for our EE inspired and longstanding experienced inmates. My questions reflect.healthy and reasonable curiosity no offense intended.
now back to the discussion.
I don't know if the 12AU7 is a voltage amplifier in this little Bravo 2
headphone amp. They don't provide a schematic which I could send to you and evaluate. The structure is clear plexiglass but I don't know whether you can see into it. The power supply is a walwart.
I am still left to wonder why the 12AU7 is even in my Jadis Da-60, an expensive amp with big "iron". The DA-60 is an integrated amp, the pre amp section uses 3 X 12AU7s and 2 X 12AX7s. (all rolled to 5751s and 7316s.) A better example of this fundamental part can be found at garage1217.com "project Ember'. You would enjoy this one because of the variety of tubes you can use with it . Makes me think it's not doing anything of critical importance.
I guess that I will just take you and Eli's word for it. My favorite pre amp is a cheap 2 tube unit, using I bet another bad choice, 6SN7s. I know the 6G8F is a better choice I have already read about that here in the asylum. However my tube collection is full of these non linear tubes. Selling then and acquiring tubes to replace them is a daunting task.
Steve
I honestly don't know why firms like Jadis use 12AU7s, ever!Down here in Aussie we have an acronym BBB. Bullshit baffles brains.
A lot of what you can read here from audiophiles and in the 'high-end' press falls under that idea. Not all of it, mind.
Here's a thought to carry with you into life. 'It depends.'
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
Edits: 07/15/15
Well after that discussion re: the relative qualities of a 12AU7 and a 12AT7 I decided to try some of my 12AT7s. And would you believe it the 12AT7s with the first trial sound great! I am not sure if the increased mu is making them sound so much better or not. I have tried a number of 12AT7s, Brimar 6060s, Siemens ECC801S, Telefunken ECC82, and Mullard CV4024. They all sound really good, I just hope I am not destroying my little amp, (which cost less than some of the tubes I have used in it.) The amp is as I said a 1 tube hybrid headphone amp designed for a 12AU7. The only complaint is that I don't have much useable play on the volume knob, an almost otherwise inconsequential movement turns it way up.
Having a longer experience with tube electronics at this juncture, I am much more hesitant to just put in any tube with a pinout that will work. This time however it seems to be the right roll.
I am so pleased with this sound that I am going to start a thread about the 12AT7.
Steve
You nailed it. It does and always will depend.
Steve
"I don't understand why so many amps are designed to use that tube, if they are so bad."
In a word, money. The more linear Noval twin triodes, whose electrical characteristics are more or less the same, use twice as much heater current. Even if we postulate that tube costs are =, doubled heater current draw increases the cost of power "iron". Corporate "bean counting" is anything but a new phenomenon.
The 12AU7 is acceptable in the "concertina" phase splitter and voltage follower roles. In those jobs, the type's fundamental non-linearity is (more or less) a non-issue, due to local current NFB. Voltage amplification is a task the 'U7 triode is bad at.
Eli D.
The overall cost of producing the amp is heavily impacted by the transformers and other related bits of hardware used. The question then becomes why does it sound good and don't other tubes need roughly equivalent components? It seems penny-wise and pound foolish.
The audio-person hobby are intensely focused on the sound quality. It would seem easy to build a better sounding amp, using a different tube, that would sell well even if it were more expensive.
Steve
The 12AU7 tube is a good choice when you need limited gain and not a ton of drive. With a CCS plate load, their performance is quite good.
In a desktop hybrid amp, if you have a ~50V DC supply feeding the thing, then don't bother rolling tubes. If it has a proper power transformer, then go for it!
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