Triode vs Pentode mode?

Discussion in 'Amps and Cabs' started by guitarlix, Dec 23, 2009.

  1. guitarlix

    guitarlix Member

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    What does this mean? See this on a lot of amps nowadays.
     
  2. Billm

    Billm Member

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    It's an inexpensive way for manufacturers to add a feature to an amp and to make a somewhat different tone available.

    Your output tubes are typically pentodes, meaning that they have five elements inside (plate, cathode, control grid, screen grid, suppressor grid). Pentodes (and beam power tetrodes, such as the 6L6/6V6 family) are very efficient... as tubes go. The screen grid eliminates the capacitance between the plate and the control grid, which makes the tube more linear and controls electron flow more accurately, for more power.

    Connecting the screen grid directly to the plate supply (same voltage as the plate) makes the tube function more like a triode, hence the name. It almost halves the maximum power, so people sometimes call it a half-power switch. The tube wastes power in triode mode.

    At anything less than full volume, the difference between full and half power is not that noticeable. It definitely does not halve the loudness of the amp.

    Triode mode on a pentode sounds thicker, mushier, less articulate. Some people think it sounds more bluesy; I think it just sounds sloppy, like the difference between sober and drunk.
     
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  3. Gnarlly

    Gnarlly Member

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    Agreed. I never liked the triode mode ("1/2 power") setting on amps I've owned that had it (ex. Marshall Jubilees). Definitely more "mushy," and not in a good way IMO.
     
  4. pjrhd28

    pjrhd28 Silver Supporting Member

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    I have a Blueverb with the Triode/ Pentode switch and its the best I've ever encountered.

    That being said, the Pentode Mode is bolder, all else (even volume) being equal. There's just a presence (and not like a presence control) that the amp has in Pentode mode.
     
  5. mark norwine

    mark norwine Member

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    I like that analogy! Can I use that?
     
  6. Billm

    Billm Member

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    My Christmas gift to you, Mark!
     
  7. Deaj

    Deaj Member

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    I didn't care for the sound and feel of the Rivera amps running the output tubes as triodes - struck me the same as Gnarlly's description. I do like it as an alternative in my Fuchs ODS however.
     
  8. FenderBigot

    FenderBigot Supporting Member

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    A great analysis by Bill M... thank you sir!

    I've tried the Vox NT with the pentode/triode switch... don't care for the amp in the triode mode, it sounds week and flimsy to me.
     
  9. WesKuhnley

    WesKuhnley Member

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    Since it costs nothing to implement, many builders like to include it, even if most players simply leave it in the pentode position.
     
  10. Fuchsaudio

    Fuchsaudio Member

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    This is very dependent on the output tube type (the tube number and brand) and on the output transformer as well. The plate resistance of the tube changes a bit in triode mode, and thus, the transformer match will change as well. I've done this in some amps that sounded amazing, and others that turned into a mushy drunken mess....(love that analogy).

    Some builders ( :) ) like disconnecting negative feedback in triode mode, which lets the amp get a little more gnarly in triode mode, although the presence control may no longer work on some amps. It's certainly fairly easy to implement in many amps, and with very little parts cost. In an old Bassman chassis, the ground switch location is a great spot, close to the power tubes,so lead lengths won't be an issue.

    An amp won't be "half as loud", but will break up sooner and smoother in triode mode.
     
  11. Pentode

    Pentode Supporting Member

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    Pentode Rocks!!! :wave
     
  12. GTRJohnny

    GTRJohnny Member

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    I must be the odd man out... I very much prefer the Triode mode in the Carr Rambler. To me, it really thickens the tone and sort of takes the amp from being milky to being more like eggnog. Speaking of which, where's my Brandy? :)
     
  13. CitizenCain

    CitizenCain Member

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    I like the triode mode in my Bugera V22. It gives the amp a nice organic sound. I think the pentode mode in this amp is a bit stiff-sounding to my ears.
     
  14. mbratch

    mbratch Member

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    On the Vox Night Train, I think the triode mode actually sounds a little richer and a little less bright (less presence) than the pentode mode. Maybe like what GTRJohnny describes with his Rambler: a little thicker sounding I think. I would not say that the triode mode on this amp sounds "sloppier" by any stretch. It sounds just as tight as pentode mode. Just a wee bit darker. I like both modes equally for different reasons.
     
  15. RJLII

    RJLII Member

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    My Carr Rambler sounds pretty good in Triode mode, but it does darken the tone up a fair bit with all else being equal. The tone controls are so effective you can fix that pretty quick though. You're able to get some power tube breakup at reasonable volumes in Triode too. I prefer the dynamics and chime of Pentode overall but Triode adds another useful flavor.

    In the words of Carr Amplifiers: "Pentode sounds loud and punchy with great headroom while Triode is more vintage and warm with very thick midrange".


     
  16. Mike9

    Mike9 Supporting Member

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    I prefer the Triode mode on my '79 UL Super Reverb. It along with other mod make it much less sterile sounding - in fact it's a great sounding amp in Triode mode.
     
  17. GrooveSlinger

    GrooveSlinger Member

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    The triode mode in my Bugera V55 is warm, sweet, and chewy. Awesome for singing leads, with SUPER harmonics.
     
  18. jimmyj

    jimmyj Member

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    I once had a Seymour Duncan convertible amp that I thought sounded very good in triode mode. I was using a strat at the time, though. I think a humbucker equiped guitar might have sounded mushy with that amp in triode.
     
  19. daramps

    daramps Member

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    I agree with Fuchs and Billm on their observations.

    Also like to chime in and say that triodes by themselves are not to blame for any percieved mushiness or darkness.

    It's just their "care and feeding requirements" are quite different.

    Triodes can deliver tremendous articulation....
     
  20. Fuchsaudio

    Fuchsaudio Member

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    Until you've heard 4 8417's triode wired for 50-W (fed by the right circuits...lol), you haven't lived.
     

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