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Mini tube internal preamp?

Discussion in 'Pickups & Electronics [BG]' started by CpTCrunch, Jun 7, 2011.

  1. CpTCrunch


    May 11, 2011
    Earth Mostly.
  2. ThrashMaster


    Jul 7, 2010
    Boston, MA
    super low voltage ie most likely wont sound all that 'tubey'
  3. I've thought about it. There are lots of really tiny tube pre designs all over the internet. But I figure it's a bad idea for three reasons:

    1. Tubes are fragile. They don't like being bounced or vibrated, especially when they're working. You could shockmount one, but that would take up lots of space in your bass.

    2. Tubes like high voltages. The higher the plate voltage, the tubier and better the sound. (I could be wrong, don't quote me on that.)

    3. Tubes generate lots of heat. Unless you're building a new bass with a special tube compartment, I'd be concerned about the heat potentially melting insulation off wires and causing shorts. Also, heat tends to degrade battery performance and life, quite significantly.

    4. (Bonus!) What's the point? Preamps in basses are there to reduce cable loading and provide onboard EQ. If you want tube tone, get a tube amp or a hybrid. It'll suffer none of the issues above.
  4. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    A lot of tube over-drive pedals use low voltage "starved plate" designs. This would likely sound like one of those. It wouldn't have much headroom, so even in the triode mode, a hot pickup would over drive the tube.
  5. Interesting. Good to know!

    But the tube will still be subjected to all the knocks and bounces of the bass, which I read that some tubes (particularly very small ones) really dislike, no?
  6. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    He said it was a low microphonic tube, but I would think it's not the best place to stick a tube. I notice it uses two batteries, an AA and a 9V, so I'm assuming the AA is for the filament. I don't know how warm the tube would get. but it seems like another reason not to stick a tube in your bass.
  7. CpTCrunch


    May 11, 2011
    Earth Mostly.
    Yea I agree, it dosen't seem like a great idea.
    Between the heat, movement factor and lack of space in many basses its not something I would try.
    Err well that and all my basses are @ 18v currently.

    Its still pretty interesting though. Its the first internal tube setup I've come across.
  8. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    Yeah, but at low voltages it's kind of a make believe tube setup. ;) JFETs will get you the same tone.
  9. Once, in my younger and more foolish days, I toyed with the idea of carving a giant chunk out of the lower body, porking the innards out of a studio-grade tube pre, and mounting 'em in there with springs for the vibration and perforated metal covers for the heat (and to see the toobz!). Power was to be supplied by a box that I would build, containing the power supply from the unit, jacked into the wall via a standard AC cord, and connected to the bass with either an XLR or Speakon cable.

    I was all set to do it, but then, all of a sudden, I decided that I had better things to do. And I never looked back! :D
  10. b_carville


    Jun 26, 2008
    A few years ago some company (Alvarez maybe) stuck a tube preamp in an acoustic guitar.
    Seems like marketing BS to me.
  11. There really isn't a lot of point, and quite a few downsides. I agree with you, Carville.
  12. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    That stuff is always best left to be external. Just stick a clean JFET buffer in the bass and then to the tube pre!

    But I did a similar thing with one of my '73 Rics back in the late 70s. I don't remember what I was going to install, but I think it was some kind of parametric EQ. Or a couple of Anderton Super Tone Controls. I did rout out the body and was putting a maple top on it so I didn't have to use a pickguard. Later I filled everything back in with maple, and that's how the poor thing sits today. I also made it fretless. I'll do something with it someday.

    It's the bass on the right. The one on the left also got a lot of mods, large frets and new paint. I'm going to restore that one soon. Ah the foibles of youth! :p
  13. 1. Alot of these sub mini valves where built to be used in submarines and missles, so tend to not be fragile.

    2. these subminis also run on alot lower voltage than a 12ax7, sometimes only needing about 50V which can be obtained easily with a 9v battery and a voltage doubler.

    3. They really don't generate enough heat to cause a problem and you're going to have ventalation aren't you so people can see your valve in your bass?

    4. This is the real issue, theres nothing in there you couldn't stick in a stomp box so it's more of a fad really, unless you wanna have some valve grind easily accessable. Also the battery life isn't going to be to great. They tend to pull the same current as the most current heavy IC's
  14. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    Good points!
  15. Mammoth - cool, good to know!

    But one further point just has sprung to mind (after reading your point about the missiles and subs); these aren't, then, really audio tubes, are they?

    I know, of course, that a triode is a triode is a triode; but aren't some tubes better suited to audio applications than others? (I base this assumption off the fact that 12AX7's, 12AU7's, EC88's, KT88's, 6L6's and others seem to have largely survived the test of time in audio gear, while others haven't.)

    So if they're rugged like you say, and draw only minimal power, like you say, why aren't our amps using them? Is it just because nobody ever felt the need, or is there actually a reason?

    I'm curious now!
  16. 12ax7 is industry standard in guitar amps, theres alot more of them about and they're cheaper. There are some amps out there that use subminis but not many since they're not made anymore.
  17. FunkMetalBass


    Aug 5, 2005
    Phoenix, Arizona 85029
    Endorsing Artist: J.C. Basses
    I'm all about onboard controls as I have a 3-band EQ in all of my basses and even an onboard tremolo. However, the notion of putting a small tube into a bass seems to be a poor decision for all of the reasons mentioned above.

    Unless there is a good reason that a tube pedal or tube pre isn't feasible, I agree with the sentiment that the onboard should be the last place to consider putting the tube.
  18. Way cool. Thanks for the info, y'learn something new every day!
  19. BassLife77


    Nov 13, 2009
    San Diego
    It looks like the seller is using the military JAN 6418 submini tube. I built one of these preamps in a box running at 30V and it sounds great. I wouldn't put it in a bass though. You need at least 27V to the tube to get a decent tone. At 9V it sounds kinda anemic for bass.
  20. They could be space charge tubes - which were designed for car radios in the 50's on low voltages.