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Post subject: 5751 Tubes
Posted: Thu Dec 12, 2019 3:21 am
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I often read on the internet that putting a 5751 tube in the pre-amp allows you to push the power section of the amp harder, or words to that effect.

Just what does that mean and what is the science behind it?

I have scant knowledge of amp electronics and to my simple mind to push a power tube harder I would have thought that you would need to feed it a stronger signal from the pre-amp. But how can lowering the gain achieve that?

I also read that a 5751 tube will make an amp quieter. From what little knowledge I do have I believe that gain and volume are two completely different things and that lowering the gain will not necessarily lower the volume. But my understanding may be wrong as a little knowledge can be a dangerous thing!


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Post subject: Re: 5751 Tubes
Posted: Thu Dec 12, 2019 5:32 am
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5751 have 70 % gain, 12AX7 have 100 % gain and it is what you may have.

You won't push harder the power section with 5751 if your amp use 12AX7

Less gain = less overdrive = little less volume output.

You may just need a good overdrive pedal.


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Post subject: Re: 5751 Tubes
Posted: Thu Dec 12, 2019 6:39 am
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stratele52 wrote:
5751 have 70 % gain, 12AX7 have 100 % gain and it is what you may have.

You won't push harder the power section with 5751 if your amp use 12AX7

Less gain = less overdrive = little less volume output.

You may just need a good overdrive pedal.


Thank you for your reply but you have not addressed the question I was asking.

I asked why people think putting a 5751 in the pre amp will make the power amp work harder. Is this a myth or if true what is the science that makes it so.


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Post subject: Re: 5751 Tubes
Posted: Thu Dec 12, 2019 6:44 am
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65Blackface wrote:

Thank you for your reply but you have not addressed the question I was asking.

I asked why people think putting a 5751 in the pre amp will make the power amp work harder. Is this a myth or if true what is the science that makes it so.


I'll ask ;
Why there are so much false information on the web ? Who know.

You did'nt give any link to that affirmation and I never read that myself .

I answer a tube with less gain ( 5751 ) can't push harder the power amp

Or people replace a defective tube ( 12AX7 ) by a brand new tube ( 5751) and think it is because it is a 5751
Or they replace the Phase Inverter tube witch is sometimes a 12AT7 ( 60 % gain)
You did not write anything about that .

Put a 5751 tube where you have 12AX7 / ECC83 on most amp can't push power amp harder


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Post subject: Re: 5751 Tubes
Posted: Thu Dec 12, 2019 8:38 am
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stratele52 wrote:
65Blackface wrote:

Thank you for your reply but you have not addressed the question I was asking.

I asked why people think putting a 5751 in the pre amp will make the power amp work harder. Is this a myth or if true what is the science that makes it so.


I'll ask ;
Why there are so much false information on the web ? Who know.

You did'nt give any link to that affirmation and I never read that myself .

I answer a tube with less gain ( 5751 ) can't push harder the power amp

Or people replace a defective tube ( 12AX7 ) by a brand new tube ( 5751) and think it is because it is a 5751
Or they replace the Phase Inverter tube witch is sometimes a 12AT7 ( 60 % gain)
You did not write anything about that .

Put a 5751 tube where you have 12AX7 / ECC83 on most amp can't push power amp harder


Thank you once again for your reply and for answering those questions I did not ask.

I am not looking to replace any tubes in my amp, I was simply asking a question to try to understand why there seems to be a commonly held view that a 5751 will work the power amp harder and I was curious to know why that might be the case unless of course it has no basis in fact.

Whilst I readily admit to being a complete novice when it comes to amp electronics, I do however have a very good knowledge of the 12??7 family of tubes. That is why I did't ask about their gain and uses.

I'm guessing you do not know why people would think that lowering the front end gain would cause the power amp to work harder be it true false.

I have never saved links to where I read the comments but if it helps then I will repeat it here and perhaps you or someone else can tell me if I am correct (and if so why) or if it is pure fiction. So here goes:

Putting a 5751 in V2 of my '65 Deluxe Reverb will lower the front gain and cause the power tubes to work harder. Is this true (and if so why) or is it bovine dung?


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Post subject: Re: 5751 Tubes
Posted: Thu Dec 12, 2019 9:50 am
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3 time and last time I'll give same answer;


" Putting a 5751 in V2 of my '65 Deluxe Reverb will lower the front gain and cause the power tubes to work harder. Is this true (and if so why) or is it bovine dung? "

1- It will lower the front gain
2 - With less front gain, power tubes can't work harder.

In other word, with less input ( gain) output tubes don't work hard.
To say more easy to understand, with no guitar plug in the amp ( no gain ) are output tubes work hard ?

Now I will stop to follow you. You look a troll


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Post subject: Re: 5751 Tubes
Posted: Thu Dec 12, 2019 9:51 am
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To get the same volume with a 5751 instead of a 12AX7, you have to turn the volume knob(s) up. A lot of people mistakenly think "higher knob settings mean the amp is working harder".
--------------
Tube swaps DO affect where distortion happens in the amp. If you put a 5751 in V1, you clean up the whole preamp somewhat. So when you crank the amp up to the same volume, more of the distortion will be coming from the power tubes.

(The power tubes won't actually be distorting more than usual -- that's a function of how big their input signal is. It's just less preamp distortion in the mix.)
---------------------
A similar falsehood/misunderstanding is that putting a volume box in the fx loop lets you "push the tubes harder". It doesn't.

The volume box was designed on the FDP to tame the abrupt low-volume response of the master volume on first generation of HRD's. Those went from silent to roaring loud between 0 and 1 on the master -- hard to control at bedroom volume. The volume box is just a second master volume to lower the signal going to the regular master, so you can turn the regular master up to its more linear range.

But when "Carl" started building and selling them, he included "lets the tubes work harder" as part of his sales pitch, and that falsehood has spread all over the innerwebz.
------------------
It's good you question what you read. "Common wisdom" is often wrong. Myths and misunderstandings abound.

You intuitively thought that lowering the gain at the first stages shouldn't make the later stages "work harder" -- you're correct.


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Post subject: Re: 5751 Tubes
Posted: Thu Dec 12, 2019 10:25 am
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Here's how the 5751 misunderstanding got started.

Stevie Ray Vaughan popularized the idea of swapping a 5751 for a 12AX7 in V1. He liked to hear less preamp distortion and more power amp distortion. Lowering the signal to the power amp actually reduces how hard the power tubes work. But a cleaner preamp signal is still big enough to cause the power tubes to overdrive, so when he cranked his amps more of the distortion was coming from the power section and less from the preamp.

He described it as "letting the power tubes do more of the work" ("the work" being "generating distortion"). It was a metaphor -- not a literal engineering description.

Imprecise, poetic phrasing by a guitar player, misinterpreted and repeated by other guitar players.

If you actually want your tubes to "work harder", you increase their input signals. A 5751 in V1 reduces the signal going into V2, which in turn reduces the signal going to subsequent stages.

Stevie was actually slightly reducing how hard the power tubes were working. But he was significantly reducing how hard the preamp was working. So a much cleaner preamp signal and a slightly cleaner power amp results in more of the distortion coming from the power amp than the preamp. So letting the power tubes do "more of the work of producing distortion", not "working harder making more volume".


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Post subject: Re: 5751 Tubes
Posted: Fri Dec 13, 2019 5:54 am
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strayedstrater wrote:
To get the same volume with a 5751 instead of a 12AX7, you have to turn the volume knob(s) up. A lot of people mistakenly think "higher knob settings mean the amp is working harder".
--------------
Tube swaps DO affect where distortion happens in the amp. If you put a 5751 in V1, you clean up the whole preamp somewhat. So when you crank the amp up to the same volume, more of the distortion will be coming from the power tubes.

(The power tubes won't actually be distorting more than usual -- that's a function of how big their input signal is. It's just less preamp distortion in the mix.)
---------------------
A similar falsehood/misunderstanding is that putting a volume box in the fx loop lets you "push the tubes harder". It doesn't.

The volume box was designed on the FDP to tame the abrupt low-volume response of the master volume on first generation of HRD's. Those went from silent to roaring loud between 0 and 1 on the master -- hard to control at bedroom volume. The volume box is just a second master volume to lower the signal going to the regular master, so you can turn the regular master up to its more linear range.

But when "Carl" started building and selling them, he included "lets the tubes work harder" as part of his sales pitch, and that falsehood has spread all over the innerwebz.
------------------
It's good you question what you read. "Common wisdom" is often wrong. Myths and misunderstandings abound.

You intuitively thought that lowering the gain at the first stages shouldn't make the later stages "work harder" -- you're correct.


Thank you for answering my question with a very good explanation.


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Post subject: Re: 5751 Tubes
Posted: Fri Dec 13, 2019 8:26 am
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As well, because of the 5751's slightly decreased gain (relative to a 12AX7) the S/N ratio is improved and the amp is often quieter at idle.

Arjay

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Post subject: Re: 5751 Tubes
Posted: Fri Dec 13, 2019 9:53 pm
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Retroverbial wrote:
As well, because of the 5751's slightly decreased gain (relative to a 12AX7) the S/N ratio is improved and the amp is often quieter at idle.

Arjay

This is why a put a 5751 in V1 in my SuperSonic 22. It slightly improved the idle noise.

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