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Thread: The 'magic' of the V1 pre amp tube

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    Default The 'magic' of the V1 pre amp tube

    I picked this up in reference to the late Stevie Ray Vaughan. his tech would change one of the pre amp tubes on his Fender amps to one with lower gain (usually 5751 ) in place of standard ECC83 so it would not distort too early on and give more clean headroom. But some advise against this as it can change the basic tone of the amp and affect other parts of the circuit too. It's been suggested the power valves then work harder-or run hotter to make up for this but I don't see how. Lower gain tube must mean it sends lower voltages to the power section in first place ? your thoughts...
    Last edited by Gold star; 09-28-2019 at 02:57 PM.

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    Imperator of Indignation idsnowdog's Avatar
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    Default Re: The 'magic' of the V1 pre amp tube

    I think the 5751 might have been in the second position? I have always used them in the second postion. The 5751 distorts in a very different way than a 12ax7 and a mix of the two creates nice overtones. You can use whatever you like. A champ with AU7 v1 and 5751 v2 is a great combo.

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    Mojo's Minions ItsaBass's Avatar
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    Default Re: The 'magic' of the V1 pre amp tube

    For almost 10 years now, I have been running a 12DW7 in the first 12AX7 spot of my main amp. I had trouble with too much early breakup on the amp, a 15W 1x12 combo. The milder tube helped quite a bit. The amp will never be a clean amp (which is why I like it), but I wanted it to start breaking up a little bit later. This seemed to do the trick.
    Quote Originally Posted by LesStrat View Post
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    I do a few chord things, some crappy lead stuff, and then some rhythm stuff.

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    PenultimateTone Member Demanic's Avatar
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    Default Re: The 'magic' of the V1 pre amp tube

    The 12DW7 is a hybrid with one side 12AX7 and one side 12AU7, correct?
    I think that I've tried one of those in my Picovalve. Went back to running 2 old National 12AX7's, but it didn't sound bad.

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    Mojo's Minions Lake Placid Blues's Avatar
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    Default Re: The 'magic' of the V1 pre amp tube

    It depends on which channel you plug into. Normal or Vibrato. On any of the brown or BF Fender amps he normally used the topography is simple.

    For both channels it is: first half of 12AX7> tone stack (EQ) > second half of 12AX7 > Phase Inverter. There is no V2 between V1 for each channel and the power amp.

    Of course a lower gain preamp tube will give a cleaner signal to the power amp. The amp might clean up better but still scream when he layed into it, because he's gonna be running the amp cranked. Another factor might be a cleaner signal through the tone stack after hitting the first half of the preamp tube pretty hard with a boost.

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    Default Re: The 'magic' of the V1 pre amp tube

    OK. Electronics is complex so you read things that are not always correct. One post I read, (not here) suggested a lower gain tube in the first position can harm other parts of the circuit and make the power section work harder as it was not designed for something like a 5751 . I doubt it if people have tried it. In my case the amp is a single channel with single volume & gain knob . ECC83 / EL84 tubes. It's actually a Vox AC10 re issue. Is the 5751 tube of higher resistance?

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    Mojo's Minions ItsaBass's Avatar
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    Default Re: The 'magic' of the V1 pre amp tube

    Quote Originally Posted by Demanic View Post
    The 12DW7 is a hybrid with one side 12AX7 and one side 12AU7, correct?
    I think that I've tried one of those in my Picovalve. Went back to running 2 old National 12AX7's, but it didn't sound bad.

    Sent from my Alcatel_5044C using Tapatalk
    I forgot the details, but it's something like that.
    Quote Originally Posted by LesStrat View Post
    Yogi Berra was correct.
    Quote Originally Posted by JOLLY View Post
    I do a few chord things, some crappy lead stuff, and then some rhythm stuff.

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    Mojo's Minions JB_From_Hell's Avatar
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    Default Re: The 'magic' of the V1 pre amp tube

    I don’t understand why the power tubes would work harder to “make up” for anything. Like they’re listening to what’s coming out, determine it’s not distorted enough, and kick into high gear to pick up the lazy preamp’s slack?

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    Mojo's Minions Gtrjunior's Avatar
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    Default Re: The 'magic' of the V1 pre amp tube

    Quote Originally Posted by JB_From_Hell View Post
    I donít understand why the power tubes would work harder to ďmake upĒ for anything. Like theyíre listening to whatís coming out, determine itís not distorted enough, and kick into high gear to pick up the lazy preampís slack?
    Iím no electrical engineer but I agree with you here. Seems to me a preamp tubeís amount of gain is what it it is. The power amp simply works with what it is given.

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    Mojo's Minions Lake Placid Blues's Avatar
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    Default Re: The 'magic' of the V1 pre amp tube

    Quote Originally Posted by Gold star View Post
    OK. Electronics is complex so you read things that are not always correct. One post I read, (not here) suggested a lower gain tube in the first position can harm other parts of the circuit and make the power section work harder as it was not designed for something like a 5751 . I doubt it if people have tried it. In my case the amp is a single channel with single volume & gain knob . ECC83 / EL84 tubes. It's actually a Vox AC10 re issue. Is the 5751 tube of higher resistance?
    Your correct, what you read is incorrect. It won't harm anything. It may affect the sound or it may not depending on the amp and how it is being used. The 5751 just has lower gain compared to the common 12AX7. In a high gain amp that gets its distortion mostly in the preamp it could reduce the buzzy sound to the distortion that can often be a problem in a high gain amp.

    The amps SRV mostly used depended on power amp distortion to get that sound. And he played very very loud, which is how you get power amp distortion going.

    The exceptions would be his Soldano SLO100 that he began using shortly before his tragic passing, and/or his Dumble amps. In these such amps the use of lower gain tube in V1 or in V2 will have a profound effect on the gain structure of the amp. It could have been used to help that amp get a bluesier tone and to help tame the high gain nature of that amp, assuming they were speaking about a high gain amp.

    Nevertheless, speaking in just general terms, the tube used in V1 of just about any amp is of vital importance, because it sets the tone at the beginning that will be amplified through out the rest the amp. Rolling in and trying different tubes, usually all 12AX7s, there as a trial and error processes, is a way of fine tuning the tone of an amp.

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    Mojo's Minions eclecticsynergy's Avatar
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    Default Re: The 'magic' of the V1 pre amp tube

    Re: power tubes working harder

    I think it's just a matter of the amp getting turned up higher since the 5751 is giving a bit less gain in the preamp.

    A little more of the drive tone would be from the power tubes vs the preamp, probably giving a slightly richer character to the breakup.

    I like the sound of 6L6s running hot, but you seldom get to work them hard nowadays.
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    Default Re: The 'magic' of the V1 pre amp tube

    OK thanks..

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    Default Re: The 'magic' of the V1 pre amp tube

    Quote Originally Posted by Gold star View Post
    OK. Electronics is complex so you read things that are not always correct. One post I read, (not here) suggested a lower gain tube in the first position can harm other parts of the circuit and make the power section work harder as it was not designed for something like a 5751 . I doubt it if people have tried it. In my case the amp is a single channel with single volume & gain knob . ECC83 / EL84 tubes. It's actually a Vox AC10 re issue. Is the 5751 tube of higher resistance?
    If what you were saying were true, no amp would have a gain knob at the input, or running it on 1 or 2 would blow it up. IME, it works just the opposite.
    Quote Originally Posted by Demanic
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    I am currently using Skullcandy headphones I found in the garbage.
    I did find the DS-1 in the garbage.
    I once found a guitar amp in the garbage, a Peavey Studio 110. It caught fire at the first gig I played it at.. But it was at the end of it, thank god.

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    Default Re: The 'magic' of the V1 pre amp tube

    The only thing I would add to that is how it (5751)distorts less in the first place ? externally it looks the same as an ECC83. I wonder if it has more resistance to the voltage applied. Maybe that's why some suggest it may have an adverse effect on other components..but again, people have tried it and not reported damage to their amps

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    Mojo's Minions beaubrummels's Avatar
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    Default The 'magic' of the V1 pre amp tube

    Quote Originally Posted by Gold star View Post
    The only thing I would add to that is how it (5751)distorts less in the first place ? externally it looks the same as an ECC83. I wonder if it has more resistance to the voltage applied. Maybe that's why some suggest it may have an adverse effect on other components..but again, people have tried it and not reported damage to their amps
    Tubes donít have resistance. They operate on transconductance. The flow is regulated by a negative voltage on the grid.

    The 12AX7 has a transconductance of 1600mhos, with a power factor of 100. The 5751 has a transconductance of 1200mhos with a power factor of 70. Thatís why the 5751 provides less gain.
    Quote Originally Posted by Demanic
    Incompetence is widespread in a world that rewards mediocrity while punishing excellence.
    Quote Originally Posted by GuitarFanatic
    I am currently using Skullcandy headphones I found in the garbage.
    I did find the DS-1 in the garbage.
    I once found a guitar amp in the garbage, a Peavey Studio 110. It caught fire at the first gig I played it at.. But it was at the end of it, thank god.

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    Default Re: The 'magic' of the V1 pre amp tube

    OK thanks; so it should not have a negative impact on the amp as some suggest. It could be that being able to open up the pre amp more with less distortion could improve tone slightly..I'm guessing !

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    Mojo's Minions JB_From_Hell's Avatar
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    Default Re: The 'magic' of the V1 pre amp tube

    It's funny and somehow comforting that (in the age of infinite information), there are still bizarre myths being perpetuated.

    My favorites from back in the day involved pickups, in that you couldn't mix active and passive, or Strat and Tele pickups.

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    PenultimateTone Member Demanic's Avatar
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    Default Re: The 'magic' of the V1 pre amp tube

    Quote Originally Posted by JB_From_Hell View Post
    It's funny and somehow comforting that (in the age of infinite information), there are still bizarre myths being perpetuated.

    My favorites from back in the day involved pickups, in that you couldn't mix active and passive, or Strat and Tele pickups.
    You can certainly mix active and passive. It's just a pita to do it properly.

    Sent from my Alcatel_5044C using Tapatalk

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    Mojo's Minions LLL's Avatar
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    Default Re: The 'magic' of the V1 pre amp tube

    This is all good (lower gain 12AX/ECC in V1), but IMO, the "magic" (mystical magical killer tube amp tone) happens when the PI tube is begging for mercy.

    Which means ya gotta crank it.
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    Mojo's Minions misterwhizzy's Avatar
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    Default Re: The 'magic' of the V1 pre amp tube

    Quote Originally Posted by Gold star View Post
    OK. Electronics is complex so you read things that are not always correct. One post I read, (not here) suggested a lower gain tube in the first position can harm other parts of the circuit and make the power section work harder as it was not designed for something like a 5751 . I doubt it if people have tried it. In my case the amp is a single channel with single volume & gain knob . ECC83 / EL84 tubes. It's actually a Vox AC10 re issue. Is the 5751 tube of higher resistance?
    By that logic, turning down your guitar's volume knob would have the same effect.

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