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Old 17th February 2012, 12:15 PM   #1
Jay is offline Jay  Indonesia
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Default What is the best use of 12AT7?

I don't understand what the 12AT7 is designed for. The higher mu 12AX7 and the lower mu 12AU7 seem to surpass the subjective quality of a 12AT7.

So my question is, do you know how to get benefit from 12AT7 "characteristics"? have you ever heard a system that sounds very good with 12AT7? Is there any situation when you decide that you are going to use 12AT7 instead of the other tubes of the same price level?

With the Aikido, the 12AT7 is suitable for the front end (low enough gain) and also for the back end (low enough Zout, especially when I use a solid state amplifier). But it is still not good enough (BTW I own several Mullards).

Is there any circuit where 12AT7 is not inferior? Simple buffer may be?
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Old 17th February 2012, 12:35 PM   #2
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Quote:
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So my question is, do you know how to get benefit from 12AT7 "characteristics"? have you ever heard a system that sounds very good with 12AT7? Is there any situation when you decide that you are going to use 12AT7 instead of the other tubes of the same price level?

Is there any circuit where 12AT7 is not inferior? Simple buffer may be?
In order: Yes. Yes. Yes. Yes. Yes, but there are better tubes for simple buffers.
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Old 17th February 2012, 12:53 PM   #3
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In order: Yes. Yes. Yes. Yes. Yes, but there are better tubes for simple buffers.
And what does that mean?

I'm trying to find the best use of them. May be not for my main system, but at least I can use them. How about the active crossover by John Broskie?
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Old 17th February 2012, 01:01 PM   #4
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By "yes," I mean "yes" to each of those questions. Yes, I know how to use 12AT7 to make good circuits. Yes, I have heard many systems that used 12AT7 that sound good.Yes, there are situations where the 12AT7 characteristics fit the application very well, but I don't know what you mean by "price level"- tubes of a given type can usually be inexpensive or expensive, according to collector value. The quality of the tube has little or no relationship to the price. Yes, it can make a good simple buffer, but there are better tubes for that.

I don't know John's crossover.
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Old 17th February 2012, 01:08 PM   #5
Jay is offline Jay  Indonesia
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By "yes," I mean "yes" to each of those questions. Yes, I know how to use 12AT7 to make good circuits. Yes, I have heard many systems that used 12AT7 that sound good.Yes, there are situations where the 12AT7 characteristics fit the application very well, but I don't know what you mean by "price level"- tubes of a given type can usually be inexpensive or expensive, according to collector value. The quality of the tube has little or no relationship to the price. Yes, it can make a good simple buffer, but there are better tubes for that.

I don't know John's crossover.
What confused me was the last sentence: there are better tubes

If the better tubes are "rare" (I'm not saying expensive okay), that's fine, but if it were 12AU7...

BTW, could you share those schematics you were talking about?

The JB's crossover is using 6922 or 6DJ8 (of course not 12AT7 )
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Old 17th February 2012, 01:23 PM   #6
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A buffer ideally uses a tube with high transconductance and high gain. The gain of a 12AT7 is very good, but the transconductance is moderate. A 6DJ8 (for example) has a better transconductance, but lower gain. Fortunately, it's linear enough to not suffer from the reduced feedback, so it makes an excellent buffer. A D3a is even better (high transconductance and high gain, couple with excellent pre-feedback linearity), but we're already well past the point of overkill for audio buffer applications.
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Old 17th February 2012, 01:38 PM   #7
Jay is offline Jay  Indonesia
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but we're already well past the point of overkill for audio buffer applications.
Yes, I was afraid so. Especially when I always insist on using good power supply. I can't imagine using expensive power supply just for 12AT7. Or may be 12AT7 is suitable for power supply itself. Something like an improved Audio Note feedforward shunt regulator?
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Old 17th February 2012, 02:05 PM   #8
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I'm not sure why you're correlating "expensive power supply" with tube choice. Or the implication that "expensive" means "high quality" or "suited for the purpose."

I did a pretty extensive analysis of simple tube buffers including calculation of power supply requirements- you can find that on my website in the Preamp section. You might find it useful.
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Old 17th February 2012, 02:22 PM   #9
Jay is offline Jay  Indonesia
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I'm not sure why you're correlating "expensive power supply" with tube choice. Or the implication that "expensive" means "high quality" or "suited for the purpose."
It is simply about the price-to-performance ratio. An expensive power supply will increase the price variable, while the choice of the amplifying tube may lower the performance variable.

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I did a pretty extensive analysis of simple tube buffers including calculation of power supply requirements- you can find that on my website in the Preamp section. You might find it useful.
Okay I will check it out... thanks.
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Old 17th February 2012, 02:23 PM   #10
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It is simply about the price-to-performance ratio. An expensive power supply will increase the price variable, while the choice of the amplifying tube may lower the performance variable.
That one has me scratching my head.
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