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The theory behind starved plate tube pedals?

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  • The theory behind starved plate tube pedals?

    The more voltage = the more headroom. So if instead of 200V you run the grid of your typical 12AX7 at 9 or 12V... Do you get instant saturation, or simply not enough voltage to allow it to run at its best?

    A lot of people mention tube pedals run on batteries or 9/12V supply are a lot marketing, little sense. Why is that? A lot of people seem to go for the starved plate system now.
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  • #2
    I think that's just it, it's all marketing. Becuase a pedal has a tube in it, it must sound better than one without a tube in it, and so we can sell it for more.
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    • #3
      I have had discussions with a couple of pedal builders in the past who have suggested that a 12AX7 in a pedal does virtually nothing at all but act as a power source but not a source of tone ... it's a total gimmick that the 12AX7 will do anything at all really.
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      • #4
        I have had discussions with a couple of pedal builders in the past who have suggested that a 12AX7 in a pedal does virtually nothing at all but act as a power source but not a source of tone ... it's a total gimmick that the 12AX7 will do anything at all really.

        I guess my ears must just be lying to me when I swap tubes in my Tube Driver and hear dramatic changes in tone.

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        • #5
          Originally posted by m-theory

          I guess my ears must just be lying to me when I swap tubes in my Tube Driver and hear dramatic changes in tone.


          Power sources can make pedals sound different but that's a whole other kettle of fish from getting tube tone into a pedals output from a 12AX7. A dying 9 volt battery will make a pedal sound different from a fresh one versus a transformer ...
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          • #6
            the "theory" is largely economics (and a bit of marketing). a unit running lower voltage is cheaper to build. 12a-7 tubes can (depending on the tube) run OK even at only 40v. lower voltages will give you less headroom and distort a little earlier, but the main reason is really that the power supply is cheaper and easier to build.

            i've not messed around with tube pedals much, but my impression is that some of the ones that run with very low voltages have a very hot buffer/preamp before the tube. i think i am right in saying this drives the tube to function a little like a low-pass filter (though would love clarification on that).
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            • #7
              Think again.

              With tubes the clipping is at the point where the tube "loses interest" in the signal and gradually changes the amount of amplification it will do. When running at high voltages a large part of the amplifying will be pretty linear and only with high signal levels one ends up in the less linear or "losing interest" part of the tubes working region. With low voltages the tube will therefore be close to non linear in it's amplification all the time, resulting in distortion straight away.

              Problem is that the output levels of the tube are, because of that lack of interest, at minimal.
              Only by feeding the tube a very strong signal something will come out. That output signal is more or less "filtered" with a tubey characteristic.
              An Ibanez Tubeking, a Fender Performer amplifier as well as a Radial tonebone therefore do very hard clipping of the signal before feeding it to the tube. The output signal is more tubelike. That's also the reason that changing the tube to anoter type (with a different characteristic) will cause a change in sound.
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              • #8
                Originally posted by m-theory

                I guess my ears must just be lying to me when I swap tubes in my Tube Driver and hear dramatic changes in tone.


                Someone on the VG-88 mailing list some years ago said that they tried a load of different valves in a Tube Driver and couldn't hear much of a difference; they then (accidentally) tried it without any tube in at all and it still sounded the same...
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                • #9
                  Originally posted by dirk-hendrik
                  Think again.

                  With tubes the clipping is at the point where the tube "loses interest" in the signal and gradually changes the amount of amplification it will do. When running at high voltages a large part of the amplifying will be pretty linear and only with high signal levels one ends up in the less linear or "losing interest" part of the tubes working region. With low voltages the tube will therefore be close to non linear in it's amplification all the time, resulting in distortion straight away.

                  Problem is that the output levels of the tube are, because of that lack of interest, at minimal.
                  Only by feeding the tube a very strong signal something will come out. That output signal is more or less "filtered" with a tubey characteristic.
                  An Ibanez Tubeking, a Fender Performer amplifier as well as a Radial tonebone therefore do very hard clipping of the signal before feeding it to the tube. The output signal is more tubelike. That's also the reason that changing the tube to anoter type (with a different characteristic) will cause a change in sound.

                  Dude that's actually really helpful! So for all tube snobs out there (like me ), a hybrid actually works better then?
                  How would you clip the signal before the tube, in a nutshell? Use something like a simple clean boost circuit in front, or would it need more gain?
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                  • #10
                    I've gone over the project many times and its just not feasible to use it in a pedal design.

                    mostly due to power suplly options, implementing it into circuit designs, you're better off with a jfet.

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                    • #11
                      A starved plate tube is basically marketing mumbo to cover up the fact that the tube is not running at typical voltages (200 - 400 Vdc). Generating the high voltage is expensive so they run the tube at 12V or so (which is cheap).

                      Running the tube at lower voltages changes its transfer function quite a bit vs. higher voltages. This is not necessarily a bad thing and does impart a different sound.

                      The tube still clips if you drive it hard enough. You can use solid-state circuits to amplify the signal before the tube.

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                      • #12
                        Originally posted by Pwn3d
                        I've gone over the project many times and its just not feasible to use it in a pedal design.

                        mostly due to power suplly options, implementing it into circuit designs, you're better off with a jfet.


                        Probably, but I know nothing about jfets and analogue stuff, and I'm really getting into tubes. I'll do some research though.

                        If I understand well though, you could easily use a clean boost in front of a starved tube pedal so that it gets boosted and more tube like, or would it typically still not be enough?
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                        • #13
                          Originally posted by Pott


                          Probably, but I know nothing about jfets and analogue stuff, and I'm really getting into tubes. I'll do some research though.

                          If I understand well though, you could easily use a clean boost in front of a starved tube pedal so that it gets boosted and more tube like, or would it typically still not be enough?


                          jfet and tube formulas are basically the same.
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                          • #14
                            My tube modded Distortion+ runs at 12v and isn't starved plate.

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                            • #15
                              Originally posted by dirk-hendrik
                              Think again.

                              With tubes the clipping is at the point where the tube "loses interest" in the signal and gradually changes the amount of amplification it will do. When running at high voltages a large part of the amplifying will be pretty linear and only with high signal levels one ends up in the less linear or "losing interest" part of the tubes working region. With low voltages the tube will therefore be close to non linear in it's amplification all the time, resulting in distortion straight away.

                              Problem is that the output levels of the tube are, because of that lack of interest, at minimal.
                              Only by feeding the tube a very strong signal something will come out. That output signal is more or less "filtered" with a tubey characteristic.
                              An Ibanez Tubeking, a Fender Performer amplifier as well as a Radial tonebone therefore do very hard clipping of the signal before feeding it to the tube. The output signal is more tubelike. That's also the reason that changing the tube to anoter type (with a different characteristic) will cause a change in sound.


                              Hi Dirk!

                              As usual, you are right on the money. HOWEVER...I just bought a seymour duncan twin tube that is getting ready to get reversed...it is using the sub-mini triodes instead of 12ax7's, and a 16 or 18v AC adaptor going into a step up transformer inside...I haven't measured the voltage yet, but it sure sounds different than your tubedriver type circuit. I'll post my findings at Aron's.

                              Talk to you later,
                              Brian
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