12AX7 vs 12AT7

herrydp · « **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 · « **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 · « **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.

goldlizsts · « **Reply #3 on:** 7 Apr 2009, 12:17 pm »

Quote from: ted_b 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

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.

cityjim · « **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 · « **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.

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 · « **Reply #6 on:** 9 Apr 2009, 08:43 pm »

Quote from: Listens2tubes on 9 Apr 2009, 02:30 am

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 · « **Reply #7 on:** 13 Apr 2009, 11:29 pm »

Yes 30db of gain for line inputs.

BillB · « **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 · « **Reply #9 on:** 14 Apr 2009, 04:05 am »

12at7 FTW!!!!!

viggen · « **Reply #10 on:** 26 Sep 2022, 10:20 pm »

Sorry for the necro. But, I just got an Oto SE which uses 12AX7. But, I have a grip of 12AT7 for my other amp, MZ3. So, for this specific amp, could I roll in 12AT7 in place of 12AX7?

For reference, my speakers are 100db/watt, so lowering gain would be a benefit.

1BionicEar · « **Reply #11 on:** 27 Sep 2022, 01:22 am »

Many people, including me, use 5751 as substitute for 12AX7. 75 gain compared to 100 for AX.
My favorites are the RCA and GE triple mica blackplates from the mid 1950s.

Ericus Rex · « **Reply #12 on:** 20 Oct 2022, 01:52 am »

Quote from: viggen on 26 Sep 2022, 10:20 pm

Sorry for the necro. But, I just got an Oto SE which uses 12AX7. But, I have a grip of 12AT7 for my other amp, MZ3. So, for this specific amp, could I roll in 12AT7 in place of 12AX7?

For reference, my speakers are 100db/watt, so lowering gain would be a benefit.

You can try them. You won't hurt anything. They probably would work fine in your setup. Let us all know what happens, especially regarding noise levels, when you do try them.

viggen · « **Reply #13 on:** 20 Oct 2022, 09:55 pm »

Quote from: Ericus Rex on 20 Oct 2022, 01:52 am

You can try them. You won't hurt anything. They probably would work fine in your setup. Let us all know what happens, especially regarding noise levels, when you do try them.

You're right it didn't hurt anything. So, I got tube swap happy. I've since used various 12AT7 and 12AU7 in the Oto's 12AX7 socket. I also did the same in two other amps. No issuel In most cases, the sound improved. No noise. Have to bump up the volume just a tad which is a plus as this gives me more range to fine tune.

rotarius · « **Reply #14 on:** 20 Oct 2022, 10:50 pm »

If the OP or someone else here is looking for a great sounding 12at7, don't forget about the variants of this tube that can be cheaper and sound better. 6201, 6414, 5965 and 7062 for example. Brent Jesse's website is a good resource. The Amperex 7062 is terrific as is the GE 5965. There are others like the 12AV7 or 12AY7 that could also be used in place of the AT7 and much cheaper. The Nos Mullard 12at7 is considered to be a benchmark for this type but I prefer a few of these variants over them.

viggen · « **Reply #15 on:** 21 Oct 2022, 04:20 pm »

Quote from: rotarius on 20 Oct 2022, 10:50 pm

If the OP or someone else here is looking for a great sounding 12at7, don't forget about the variants of this tube that can be cheaper and sound better. 6201, 6414, 5965 and 7062 for example. Brent Jesse's website is a good resource. The Amperex 7062 is terrific as is the GE 5965. There are others like the 12AV7 or 12AY7 that could also be used in place of the AT7 and much cheaper. The Nos Mullard 12at7 is considered to be a benchmark for this type but I prefer a few of these variants over them.

Thaks Rotarius (almost read rotavirus). Since this issue came up, I started frequenting Brent Jesse's site. I didn't purchase from him but I have some tubes that were sourced from him by way of buying an amp from someone who did buy from Brent. And, these tubes are some of my favorites. I did pick up a pair of 6829 GE 5 Stars that I learned about on Brent's page. These are about a third inch taller than 12at7 tubes and provides, as Brent puts it, a rich and creamy sound.

ceylon · « **Reply #16 on:** 4 Jun 2023, 09:28 pm »

Quote from: BillB 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.

12AT7 is not a 12AX7 substitute. significantly different specs. very different tubes. there are some circuits which can run avariety of tubes, but such compatability is a manufacturer question as these tubes (12ax7, 12au7, 12at7, 12ayz, 12bh7 and so one) are not substitutes for each other and their specs are not compatible. now 5751 is not a drop-in replacement for 12ax7 but it almost is. its compatibility is circuit-dependent.

ceylon · « **Reply #17 on:** 4 Jun 2023, 09:30 pm »

Quote from: rotarius on 20 Oct 2022, 10:50 pm

If the OP or someone else here is looking for a great sounding 12at7, don't forget about the variants of this tube that can be cheaper and sound better. 6201, 6414, 5965 and 7062 for example. Brent Jesse's website is a good resource. The Amperex 7062 is terrific as is the GE 5965. There are others like the 12AV7 or 12AY7 that could also be used in place of the AT7 and much cheaper. The Nos Mullard 12at7 is considered to be a benchmark for this type but I prefer a few of these variants over them.

6414, 5965 and 7062 are not drop-in replacements for 12AT7. theyre in the family of 12At7 but their compatibility is circuit-dependent.

jjss49 · « **Reply #18 on:** 6 Jun 2023, 12:45 am »

it is funny when i see folks these days saying well this tube can just sub for that, easy peasy

it is like people were bumbling idiots back then... just randomly developing and manufacturing different tube types, for the hell of it, despite them all being the same, doing this just randomly ...

dB Cooper · « **Reply #19 on:** 6 Jun 2023, 12:47 pm »

Quote from: jjss49 on 6 Jun 2023, 12:45 am

it is funny when i see folks these days saying well this tube can just sub for that, easy peasy

it is like people were bumbling idiots back then... just randomly developing and manufacturing different tube types, for the hell of it, despite them all being the same, doing this just randomly ...

Yes, it seems like many would rather ask anybody except the person(s) who should know: The manufacturer (assuming they're in business; they come and go).
BTW in most circuits (from my understanding reading those who DO know) the signal that is amplified isn't the input signal- its the difference between the input and the feedback signal. Therefore when you change the gain in the circuit this way, you're also changing the amount of feedback present in the circuit. This can have unintended consequences. Do you really trust
the 'Pin-the-tube-on-the-circuit' approach, or would you rather call the mfr and make sure (especially if your component is under warranty)?