Different tubes and tonal differences outside of gain.

Discussion in 'Amp Tech Center' started by Singles Forever, May 31, 2019.

  1. Singles Forever

    Singles Forever TDPRI Member

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    So I know the various gain factors for 12ax7, at7 Au7 etc, but my question is this:

    Outside of clean breakup threshold, max levels of drive etc., do different tubes have an effect on general tone? As in, more or less mids, more aggressive, scoopier, sweeter, harsher, spongier... or any other general words used to describe things of a tonal nature.

    I'm asking because a guitar tech friend of mine recommended that I put a 12au7 tube inside the preamp socket of a blues junior to make it 'sweet like a princeton' lol. But then another guitar tech told me that literally, all it would do is give me less gain/volume. What are your thoughts?

    Thanx!
     
  2. JD0x0

    JD0x0 Poster Extraordinaire

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    Really hard to generalize in this way because those tubes have different bias points, and different 12AX7 amps will have different bias points, so popping in a specific tube type might give different sonics in different amps.


    I will say there tends to be a misconception with lower gain tubes and 'headroom' Many think you 'increase headroom' with a lower gain tube, but that's just a perceived effect due to the lower gain. In many cases you could technically reduce headroom, with a haphazard tube swap, as the 12AX7 may have been center biased (for max headroom) and when you throw in another tube, it will likely not be at the center bias point and therefore have less headroom and more THD, which may affect the tone.

    To expand on that, if the tube is distorting more, the harmonic content has a bearing on the tonal character. Certain overtones may make a tube sound brighter, certain harmonics may make it sound a bit more mellow.. Or, the increased current of a lower gain driver tube may pull the plate voltage way down and make the sound dark(er).

    Really depends what he means by 'sweet' as well. That's a pretty broad term. I assume he means smoother and more tame overall?



    A 12AU7 is a driver tube with very little gain. It might sound good, it might not. (I'd bet on the later, unless you're hitting the amp with an active preamp or pedal, like a compressor or clean boost) Preamp tubes are relatively cheap and easy to swap and you're unlikely to hurt anything. I'm sure there'll be a couple people who have tried these swaps to 'clean up' their amps and can chime in. I'm sure they'll be a couple who were really happy, and a couple who thought the change was 'meh'
     
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  3. Dixon in Korea

    Dixon in Korea Tele-Meister

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    I put a 12au7 (or 12at7—don’t remember which right now) in my Blues Jr. III in order to give me finer control over the “edge of breakup” gain level, and that’s exactly what it did, but that’s all it did. I didn’t notice a change in tone. It definitely didn’t make the amp sound like a Princeton (I also have a silverface Princeton Reverb).
     
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  4. Cgci

    Cgci TDPRI Member

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    I put an At7 in V1 and an Au7 in v3 of my, 3x12ax7 el84 amp and it changed the feel and tone a ton. I really liked it. It was aggressively midrange heavy and boxy sounding, now it’s a little scooped, mellower and has a slight sag to it. Really nice change to my ears.
     
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  5. Axis29

    Axis29 Poster Extraordinaire Ad Free Member

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    Simple answer yes. Different tubes can change perceived 'tone' or 'feel'.

    Is it measurable? Probably not.
    Is it predictable? Not consistently.
    Is a lot of it marketing hype? Could be!

    Realistically, if you read tube dealers' stuff, you'd think you could throw a different power tube in and make your Fender sound like a Dumble, or your Marshall suddenly as clean as a Dual Showman. But, it's not so cut and dry. Some amps respond to tube swaps better. Some tubes make a bigger difference. But, honestly, none of it is night and day, and very seldom can the differences be noticed when the rest of the band kicks in. Even changing tube types (i.e. EL34's for 6L6's, etc.), may not overcome the character of the circuit.

    I find that I prefer vintage 12ay7's in V1 of my tweed amps. I really like Bugle Boys, RCAs, GEs, etc. Each one has a very subtle difference. But, I also find I like them over some of the modern ones I've tried. But, that doesn't mean what's right for me is right for everyone else. What I like to hear and feel form my amp is probably very different than a lotta folks around here.

    12ax7's? Holy crap, there are so many... old, new, and they each have their own thing going on. Some can sound warmer, some brighter, some do have higher gain (within certain tolerances, etc.) and different construction... All of it will have an effect. But, very few will give drastic results.

    A speaker change will have so much more effect on the tone. Let me repeat that... a speaker swap will have a much, much greater effect on tone, than any tube swaps you ever make.

    But, tube swapping can be fun, frustrating, entertaining or drive you wildly crazy.

    Sometimes it is that last 2% that can motivate you to play something differently. Sometimes you just an't tell.... LOL
     
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  6. Teleterr

    Teleterr Friend of Leo's

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    An AU7 is ALWAYS distorting more than an AX7. W the same bias you get the same headroom, it just takes more input volume to run out of it. AU7 sound really good IMO, but thats subjective. And theres a little tone change due to plate Z as well. AU7 tend to sound thicker, bigger, larger sound stage. etc; just more 3D. Have you heard a Twisted Tele neck p-up. It has that quality. Super cheap as NOS.
     
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  7. Singles Forever

    Singles Forever TDPRI Member

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    Okay so I actually ended up trying it, and I made recordings of both tubes. The results were interesting. The 12Au7 didnt cause the amp to have less volume as many pros claim. In fact, it was a very tiny dip, if anything. The recordings show the same size waveform with the master volume on 10 and gain around 6.5. Clean breakup didn't change much either. This could have a lot to do with the way the blues junior is made. The person who recommended this to me said that too.

    I definitely hear a tonal change, and I definitely have a preference for one of them.

    If anyone is interested in hearing the difference, I could post the recordings.
     
  8. Singles Forever

    Singles Forever TDPRI Member

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    "A speaker change will have so much more effect on the tone. Let me repeat that... a speaker swap will have a much, much greater effect on tone, than any tube swaps you ever make."

    Totally. I also just changed the speaker on this amp. I went from a Redcoat Wizard to a Heritage G12. I can't express in words how much I prefer the heritage g12 in this amplifier. It just sounds so much more 'fender' and appealing. A wizard in a blues Junior sounds much too loud, mid-range heavy, aggressive and just all-around cold. I never played through this amp..Now I use it constantly.
     
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  9. 3-Chord-Genius

    3-Chord-Genius Poster Extraordinaire

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    I have only seen different tubes make a difference in two areas:

    1) Gain
    2) Tone, but let me be specific: They do not change the tone of the amplifier. They may increase or decrease treble, but that's all I've ever heard happen.
     
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  10. Silverface

    Silverface Poster Extraordinaire Ad Free Member

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    What 12AU7 did you use? A new one, a NOS tube, a used tube and what brand?

    You could try the same tube swap with 10 different 12AU7's and get 10 different results.

    "Google" comparisons of currently available 12AX7 tubes for an example of the differences in gain and tone for a particular tube type (only because I don't recall seeing one for 12AU7's as not many are currently made).

    A tube-type swap based on a single tube is far too small a sample size to for anyone to state any kind of predictable results.
     
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  11. beninma

    beninma Friend of Leo's Silver Supporter

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    I've seen marketing information claiming some 12ax7 models have more treble/bass/mids than others.

    I did a JJ -> EHX swap on my amp when I thought it would be good to change the tubes. My impressions kind of match up with the marketing information, but it could be in my head.
     
  12. jrblue

    jrblue Tele-Afflicted

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    JD0X0's description fits my experience. I use small combo amps and do lots of tube swapping. Other than gain differences, I find no really predictable outcomes of swapping. You just have to try the actual tube in your actual circuit to see what, if anything, may result. I have a seriously modded, fantastic first-run Pro Junior, and it is totally sensitive to tubing. I consider this amp to be way to fizzy and hot up front, and use 12AU7s in it. I've used NOS vintage, new tubes, all brands, you name it. RCA cleartops? Great tubes, supposedly, they howl like banshees in this amp. Others? Some are dull, some are great, some are responsive, some are not. I finally settled on new Psvanes, which are amazing -- in this specific amp, as modded. Try 'em in something else, and it's a dice roll. So I say yes -- preamp tubes can make a big difference, but much of it is unpredictable, and unless you are going to try a whole bunch, I wouldn't even go there. People often convince themselves that the specific tube they changed was somehow the perfect one, but that's pure self-delusion. There's no such luck.
     
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  13. Singles Forever

    Singles Forever TDPRI Member

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    The tube was brand new and it's an electro-harmonix 12AU7.
     
  14. Singles Forever

    Singles Forever TDPRI Member

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    Well I definitely don't think it's the perfect tube per say. However, there is definitely a difference and I prefer the 12au7. There's less mids, and like my friend said it has a sweeter sound. There was a very slight harshness to the 12ax7 that is absent in the Au7. The amount of drive is similar, and the volume is almost as loud... but even that is debatable since the waveforms came up even in Cubase.

    I would describe the sound as non-invasive, mellow, scoopier, softer, prettier and even brighter despite all that.

    I watched a video on YouTube where a guy put 12au7 in place of a 12ax7 in the preamp section. But for some reason his amplifier went from overdriven with the ax7 to completely clean with the au7. In other words, the Au7 removed almost all of the overdrive potential and turned it into a clean amp.

    I'm wondering what there is in the blues Junior circuitry that prevents that from happening.
     
  15. archetype

    archetype Fiend of Leo's Silver Supporter

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    Tone? You may have your own perceptions, but saying that tubes do not change the tone (other than treble) of the amplifier is rong.

    Just because you don't perceive the degree of harmonic distortion, where it occurs in the audio spectrum, doesn't mean it doesn't exist. It's quantifiable. Thousands of us have been rolling tubes to get closer to the tone we want. Some of what we "hear" is grounded in confirmation bias, but the majority of what we hear isn't wishfull thinking, it's reality.

    Why do you say what you say? Explain why we're rong and you aren't.
     
  16. 3-Chord-Genius

    3-Chord-Genius Poster Extraordinaire

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    I'm not saying you're rong, but simply what I have observed. I've seen different tubes in the same amp make a difference in the amount of gain available in the preamp, and sometimes they add or remove a little high-end. That is what I've seen. I've never seen tubes change the overall tone of the amp. Perhaps other people have observed more than I have, but as for me, the only differences I've observed are what I described above.
     
  17. Teleterr

    Teleterr Friend of Leo's

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    Note that the AX7 curves are more linear than the AU7. A little more distortion/compression. I ve hear a difference in quality every times I ve done it. I think having a AU as the first tube is the most noticable due to the gain difference.
    I switch out AXs for AUs in my Pignose 40 to tame it, but it needs tweaking to get a more normal eq. Maybe plate R is a factor? Just sounds too much compressed/mellowly distorted.
     
  18. archetype

    archetype Fiend of Leo's Silver Supporter

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    Cool. With some amps it works the way you've observed.

    Also good to see that you are spelling rong right. :D
     
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  19. FenderLover

    FenderLover Friend of Leo's

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    If we swap a AU7 or AT7 into a (center-biased) gain stage designed for an AX7, I guarantee that it will be biased cold. A gain stage center-biased for a AX7 is usually intentional, while swapping an AT7 or AU7 in the same position without re-biasing will will barely be conducting, bias shifted, prone to clipping one phase well before the other.

    Swapping a AT7 or AU7 into an AX7 position that is not center-biased is real unpredictable if one is just rolling tubes. The bias may actually be moved back to center, or moved even farther from center, producing two completely different responses. >That is why generalizations cannot be made unless we talk about a specific circuit.<

    Getting less gain might be the target, but I have found it's better to have excess gain and throw some away than try to operate at half-throttle to reach what is desired. The gain is instrumental in creating the harmonic and intermodulation products that we crave, while less gain and more linearity is the stuff of HiFi circuits. Pick your poison, there's no accounting for taste. We like what we like.
     
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  20. teleman1

    teleman1 Tele-Holic

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    Every one says 12au7. What about 12au7A's. Are you lumping them together in your to example?
     
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