[guest1632]

Hi Frank and company,

Often times I see people doing tube rolling with the 12??7 tubes with 5751's. Generally, the results have been favorable. Just curious, only, any reason why you are using the 12??7 tubes versus the 5751's? I forgot which 12??7 tubes you were using. That's why the ??. My apologies there. I know the gain of these 5751 tubes are not at high as the standard tubes. Anyway, I just thought I'd ask. It's always interesting why an audio designer chooses what he wants. Thanks for your time.

Ray

[avahifi]

The 5751 tube is essentially a "ruggedized" version of the 12AX7 with lower open loop gain designed for portable equipment years ago.  Substituting for a 12AX7 will typically decrease the open loop gain of the circuit in question, thus reduce the feedback, and thereby increase the harmonic distortion.

Most of the musical differences you hear will be actually "oh boy I like more distortion."

Years ago, we did use GE NOS 5751 tubes in our factory supplied Super Pas Two preamps, because at that time we simply could not find a decent 12AX7 tube at a rational cost.  Now that many vendors have come back on line with excellent 12AX7 tubes, that issue has been mute for years.

New old stock clean room Telefunken and Mullard tubes are probably even better than what we are suppling now (mainly JJ Electronic - Tesla) brand.  However I doubt if you want to pay $100 or more each for these tubes and availability is too limited to consider them for standard production, and we certainly do not want to stock them at these prices.

Frank Van Alstine

[guest1632]

The 5751 tube is essentially a "ruggedized" version of the 12AX7 with lower open loop gain designed for portable equipment years ago.  Substituting for a 12AX7 will typically decrease the open loop gain of the circuit in question, thus reduce the feedback, and thereby increase the harmonic distortion.

Most of the musical differences you hear will be actually "oh boy I like more distortion."

Years ago, we did use GE NOS 5751 tubes in our factory supplied Super Pas Two preamps, because at that time we s ...

Hi Frank,

Interesting. So how come if the 5751 has higher gain, why is it when people sub them out from the 12ax7 the gain is lower. I'm just curious, because it seems that every review of using this tube versus the 12ax7 seems to yield a more detailed and open presentation. Hey, I am just reading what others have said. It does seem to be somewhat consistent. not interested in higher distortion.

Ray

[doug s.]

ray,

if i am reading frank's posting correctly, *yure* not - i think he's saying the 5751 has lower gain than the 12ax7...

doug s.

[guest1632]

ray,

if i am reading frank's posting correctly, *yure* not - i think he's saying the 5751 has lower gain than the 12ax7...

doug s.

Hi Doug,

Silly me. I for some reason did not read his post correctly. Well, that still doesn't explain the more detailed presentation of the 5751. At least, that's what I have read. I'm not the designer. So I'd think Frank would know best.

Ray

[doug s.]

ray,

if i am reading frank's posting correctly, *yure* not - i think he's saying the 5751 has lower gain than the 12ax7...

doug s.

Hi Doug,

Silly me. I for some reason did not read his post correctly. Well, that still doesn't explain the more detailed presentation of the 5751. At least, that's what I have read. I'm not the designer. So I'd think Frank would know best.

Ray

i am not an engineer either.  but, from what i have read, lower feedback can increase perceived detail openness of sound.  *and* distortion.    the question is how much distortion.  folk will argue about how much distortion is ok, & at what level it will colour the sound.

doug s.

[avahifi]

The 5751 tube is indeed lower gain.

Lots of people like higher harmonic distortion.  In the absence of understanding what they are listening to, they assign lots of different virtures to distortion pretty much randomly.

To "muddy" the waters further, all things being equal, when you reduce the feedback by using a lower gain active device, you will actually reduce the transient intermodulation distortion, which is excess feedback related.  This will reduce any preceived "edge" or "grain" in the sound.

Thus the best sounding tube for you with most equipment will be the one that produces a nul in both harmonic distortion (gain too low - muddy) and TIM (gain too high -  bright).  Unless of course you really like one or the other distortion aspects a whole bunch (some do).

In AVA tube equipment we design so that TIM cannot occur at all, thus all other things being equal, the best tube will be the highest gain tube possible, that is unless you really like harmonic distortion.

Now of course all you need is a high quality tube tester to find those high gain tubes, unless you are satisfied with the testing and selection we have already done for you in our new products.

Frank Van Alstine

[guest1632]

The 5751 tube is indeed lower gain.

Lots of people like higher harmonic distortion.  In the absence of understanding what they are listening to, they assign lots of different virtures to distortion pretty much randomly.

To "muddy" the waters further, all things being equal, when you reduce the feedback by using a lower gain active device, you will actually reduce the transient intermodulation distortion, which is excess feedback related.  This will reduce any preceived "edge" or "grain" in the sound.
 ...

ok, Doug and Frank. I take it them, you've taken the guess work out of tube rolling. There's no need to do any at all. So that being the case, is it possible to buy an extra  set of tubes through you? I'm not in to distortion.Hence the buyer of extra tubes question. What do you figure the average life span is for these tubes?

Ray

[MarkM]

Life span should be in the ball park of 2 years.

[doug s.]

...I take it then, you've taken the guess work out of tube rolling. There's no need to do any at all. So that being the case, is it possible to buy an extra set of tubes through you? I'm not in to distortion....

hi ray, *i* never said tube rolling isn't worthwhile!    i have had mixed results - sometimes beneficial, sometimes not.  yust may wanna stick w/12ax7's in this case.

but mebbe not - as for distortion, i wouldn't write it off completely,  sometimes people *do* subjectively prefer a bit of it.  even if it makes no sense on paper.  i used to own a mesa baron amp.   (i wish i still did - it suffered at the hands of a domestic dispute - oh well.   )  anyway, this amp had adjustable negative feedback & adjustable triode/pentode settings.  the least distortion was when it was set to 8db of neg feedback & full pentode.  my preferred setting was 2/3 triode-1/3 pentode, & 0db negative feedback.

ymmv,

doug s.

[WEEZ]

I must be missing something, 'cause the 5751 tubes are, as pointed out, lower gain tubes than 12AX7's, but the AVA gear uses 12AT7 tubes. So if lower gain is wanted; wouldn't a 5965 be substituted?

I can understand wanting lower gain in the line section, maybe. But 12AX7's are used in the optional phono section, right? I would think that the 12AX7 would still be wanted there- to obtain 40db or so of gain.

There are options for less than $100ea for NOS tubes out there, but $50 ea. is not uncommon.

The JJ 12AT7 is a great tube. And reasonably priced. I've heard that Svetlana 12AX7's are great also, but not sure about their use in a phono application.

I don't think a 12AX7 would substitute for a 12AT7, though. But I could be wrong.  

WEEZ

[guest1632]

I must be missing something, 'cause the 5751 tubes are, as pointed out, lower gain tubes than 12AX7's, but the AVA gear uses 12AT7 tubes. So if lower gain is wanted; wouldn't a 5965 be substituted?

I can understand wanting lower gain in the line section, maybe. But 12AX7's are used in the optional phono section, right? I would think that the 12AX7 would still be wanted there- to obtain 40db or so of gain.

There are options for less than $100ea for NOS tubes out there, but $50 ea. is not uncommon.

Hi Weez,

Well, I had understood that the 12ax7 was used in the main circuit. Wasn't interested in a lower gain tube here, just wondered why it wasn't used versus the 12ax7. Everything I had read suggested that the 5751 was a bit more open sounding than the 12ax7. Frank said there was higher distortion with that tube. Ok, I'm satisfied with his answer. It was just a curiosity, that's all.

Ray

[avahifi]

We use a 12AT7/ECC81 tube in the line section because it has higher current drive which is more important than higher open loop voltage gain in this application.  The closed loop gain is set at 20 dB and there is plenty of voltage gain to close the loop and provide excellent performance in the line section.

In the phono section, the closed loop gain varies from very little at high frequencies to about 60 dB at low frequencies to following the RIAA feedback loop.  Here the higher open loop gain of a 12AX7/ECC83 tube is absolutely necessary to close the
RIAA feedback loop properly.

Different tube types are used for different application needs. Do not assume that a given tube type is suitable for your circuit unless you understand the engineering requirements of the circuit.

A race tire from a Formula One car is not going to give you better handling on your hot BMW road car.  One reason you may have overlooked, F1 wheels are just 13" in diameter.  Not going to work too good on your 18" alloys.  

Frank Van Alstine

[guest1632]

We use a 12AT7/ECC81 tube in the line section because it has higher current drive which is more important than higher open loop voltage gain in this application.  The closed loop gain is set at 20 dB and there is plenty of voltage gain to close the loop and provide excellent performance in the line section.

In the phono section, the closed loop gain varies from very little at high frequencies to about 60 dB at low frequencies to following the RIAA feedback loop.  Here the higher open loop gain of a 12AX7 ...

Hi Frank, Actually, that's all I was asking for. I don't pretend to understand tube design gear, but it is always interesting why people do what they do. Everybody takes you to taks because you don't share is the belief about power cord and interconnect cables. So what. I was asking merely because out of curiosity from someone who obviously knows his stuff. I did not in any way mean to put you in a defense mode. One of the nice thing about these forums is you can yack with the manufacturer of some pretty good gear.

Besides, why would you want to use smaller wheels on your car? There's a lot more to handling than just the tires. That's obvious, and it's obvious to both of us you know that too.

So since you mentioned gain, why is it that a tube preamp seems to have to have a lot of gain? My SS pre has a choice off 0, 6, and 9.5. That is also dependent on the amp used and so on. I ask the questions because I honestly want to learn and not bash. Thank you, Sir, for your time.

Ray

[avahifi]

Essentially, industry standard is a voltage gain of 10 (20dB) on a preamp line section and 40 dB at 1K Hz on a phono section and so we designed for industry standard to be compatable with most well designed equipment out there.  That simple.

Frank Van Alstine