12AX7 vs 12AT7

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herrydp

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12AX7 vs 12AT7
« on: 18 Jan 2009, 03:14 pm »
Hi Guys,

I want to know the difference between 12AX7 tubes and 12AT7 tubes.  I know that both are triode preamplifier tubes.

I'm asking this because I own preamplifier who use both tubes.  The difference is 12AX7 is for phono channel and 12AT7 is for main channel.

Since I want to replace with mullard tubes, should I change both or just 12AT7 because I didn't use phono.

Best wishes,
Herry

ted_b

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Re: 12AX7 vs 12AT7
« Reply #1 on: 18 Jan 2009, 03:34 pm »
First off, the phono section is separate from the line stage and is not involved if you don't listen to phono.  You can change the line stage only.

Second, the 12AT7 and 12AX7 are cousins, with different gain factors.  The "X" is the highest gain of that family, at, 100.  The "T" is 30% less gain (need to turn up further for same output).  See this:
http://thetubestore.com/gainfactor.html

Listens2tubes

Re: 12AX7 vs 12AT7
« Reply #2 on: 7 Apr 2009, 10:29 am »
What tubes are you currently using in your pre? I tried a few before settling on my picks.  8)

goldlizsts

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Re: 12AX7 vs 12AT7
« Reply #3 on: 7 Apr 2009, 12:17 pm »
First off, the phono section is separate from the line stage and is not involved if you don't listen to phono.  You can change the line stage only.

Second, the 12AT7 and 12AX7 are cousins, with different gain factors.  The "X" is the highest gain of that family, at, 100.  The "T" is 30% less gain (need to turn up further for same output).  See this:
http://thetubestore.com/gainfactor.html

Hello,

I'd like to ask a not-so-smart question.  What 12A? tubes are of the "lowest' noise type/brand? for use say in a preamp circuit.

Apreciated. :thumb:

cityjim

Re: 12AX7 vs 12AT7
« Reply #4 on: 8 Apr 2009, 07:37 am »

 The 12AX7 is a hi Mu tube . Is has high gain which = high noise .

 Something like a 12AU7 is more ideal . Especially in a line stage . 98% of people have too much gain already . Is your volume knob at 9 o' clock ? If so you have excessive gain .

 The 12AX7 and 12AU7 are NOT interchangeable . Look at the datasheets . 12AU7 takes more current . Look for a 6SL7 or 6N1P tube based preamp .


cityjim

Listens2tubes

Re: 12AX7 vs 12AT7
« Reply #5 on: 9 Apr 2009, 02:30 am »
In my T8 the 12AT7 line stage produces 30dB of gain, the 12AX7 phono stage is 40dB. My volume control for CD and tuner is 10 o'clock for moderate volume 11 for high volume and 11:30 for concert (neighborhood listening through closed windows) volume. It's turned up a bit higher for the .26mV Karat even with an extra 26dB trannie for a total of 66dB of gain. Moderate volume is 11 o'clock, concert around 12:30. Would be closer with more like 30dB added. :o This is where all RCA grounding must be good/tight for best performance. I find the Mullard Master Series 10M 12AX7A's to be superlative in this case. Enjoy.

turkey

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Re: 12AX7 vs 12AT7
« Reply #6 on: 9 Apr 2009, 08:43 pm »
In my T8 the 12AT7 line stage produces 30dB of gain, the 12AX7 phono stage is 40dB.

But the gain is really set by the feedback in this case, so it's not due to the choice of tubes as such.

Is the line stage really 30dB? 20dB is more normal.

Listens2tubes

Re: 12AX7 vs 12AT7
« Reply #7 on: 13 Apr 2009, 11:29 pm »
Yes 30db of gain for line inputs.

BillB

Re: 12AX7 vs 12AT7
« Reply #8 on: 14 Apr 2009, 12:52 am »
A lot of people consider the at7 the best sounding of the 12a_7 series.

I find them good subs for ax7 if you dont mind a tiny bit of gain loss (it does not translate to 30%) and are generally mucho cheaper.

I have heard those saying that au7s do not sound good but I think the military ones (5814 and the like) sound pretty good so I don't put too much weight into that theory.

Tyson

Re: 12AX7 vs 12AT7
« Reply #9 on: 14 Apr 2009, 04:05 am »
12at7 FTW!!!!!