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If amp only accepts 6l6 tube, is a bias necessary for new tubes?

Discussion in 'Amps and Cabs [BG]' started by AckAckAttack, Nov 28, 2006.


  1. AckAckAttack

    AckAckAttack

    Aug 27, 2006
    Hello, I tried to do a bit of searching before I posted this, but I couldn't find exact information, but if there is a forum that does have this information, please feel free to direct me there and I'll close this one...

    Anyways, I need a new tube for my amp.. its an old Peavey Butcher (I know its a guitar amp, but I like it for recording at low volumes on bass, and I use it for guitar loudly too). Anyways, this amp only takes 6l6 tubes, and I had read somewhere that if an amp only takes 6l6 tubes then you do not have to bias them when you put it in? I didn't think this sounded right, because if you used different tubes, then they need to be biased, correct?

    Please fill me in if you can, all information is greatly appreciated.
     
  2. Ideally U should get it biased! the new tubes will most likely be different to the older ones-I'm NO tech , so.....- Even if U get the same brand 6L6, they can be differeing in their .....sumthin' .... so short answer- YES U NEED to get it biased.
     
  3. joegeezer

    joegeezer

    Mar 9, 2005
    Northern Wisconsin
    Avatar Club#12 Eden Club Lucky# 13--USA Peavey Club#37 Carvin Club#5
    From what I've read , the answer is also YES.
     
  4. BbbyBld

    BbbyBld

    Oct 13, 2005
    Meridian, MS
    On the Butcher, the bias is set so that you can safely replace tubes without having to worry about re-biasing. This is not ideal for performance, but it will work and be reliable...that was the philosophy at the time.
     
  5. Alot of amps have a fixed bias, i know my trace elliot guitar amp does, (well it has a switch for 6L6 and EL34). And my Peavey Classic 30 is just a clean drop in of new tubes.

    With guitar amps (and lowered powered bass amps) i dont think the bias needs to be as accuratly set as with higher powered bass amps, down to the fact that the guitar amps arent handling as much power. I think a fixed bias is usually set a tad on the conservative side aswell, so you may not be getting the fullest from every set of tubes, but i may be wrong?
     
  6. A9X

    A9X

    Dec 27, 2003
    Australia
    Fixed bias is actually the adjustable one, and cathode bias is fixed by the value of the cathode resistor in the circuit (and it's other operating parameters). Who said electronics was logical?

    I googled and couldn't find a schematic for the Peavey Butcher online, but found some suggestions to email them and ask for one. I'd do it but they'll likely ask for a S/N to get the version correct and I can't provide that. If you get one, then PM me for my email and forward it, and I'll tell you if it's a fixed bias amp and consequently needs an adjustment.
     
  7. Scottgun

    Scottgun

    Jan 24, 2004
    South Carolina
    Drop 'em in and don't worry about it unless they sound bad. If you are just a bass player and just want to be a bass player, don't get too concerned with bias. If you are a tweaker-type and enjoy poking around with the amp, find an electronic guy and see if he can install something that will let you bias each tube and have a field day. It all depends on what you like to do. In my case, my Sunn has a single bias and balance switch and I have a little multi-meter and occasionally tweak it. I know I guy that can make so I can balance each one, but that is more than I want to fiiddle with.
     
  8. BbbyBld

    BbbyBld

    Oct 13, 2005
    Meridian, MS
    It doesn't have to be.

    The Butcher is fixed, fixed bias.

    It doesn't HAVE to be re-biased, but if you want the absolute best performance, take it to a good tech and if he's worth anything he can set the bias by modifying the circuit. Otherwise, replace the tubes and wail away.
     
  9. A9X

    A9X

    Dec 27, 2003
    Australia
    I am aware of this. Merely making a point that the traditional nomenclature is not so obvious to someone who doesn't know how a circuit operates.
     
  10. AckAckAttack

    AckAckAttack

    Aug 27, 2006
    Thanks everyone, very informative, yeah I had heard that for the butcher you didn't really need it, so I'll just throw a few of them in there, see how it sounds, and if it sounds off or not loud enough then I'll take it to a tech, but if not I'll just leave them as be.

    Also, do you think JJ 6L6's would work well with this amp? I've never been in the market for 6L6's before, but I've heard JJ's are good stuff? Please let me know what you think. Thanks!
     
  11. BbbyBld

    BbbyBld

    Oct 13, 2005
    Meridian, MS
    JJ makes great tubes. I've never tried the 6L6, but I'm sure it would work fine.

    Another good one is the Sovtek, that's what we would put in it if you sent it in.
     
  12. Haha, well, wow, that is a tad confusing, well, mine are fixed fixed biases :smug:
     
  13. Not a good idea. It should be checked (among other operating parameters), and adjusted if necessary, regardless of output, whether you play guitar, bass, or both. If you care about your equipment then do the right thing. If you don't care about it sounding good, or melting down, then go ahead and trash it.

    In many cases from the factory this happens, but there also instances opposite to this.

    I don't have the schematic in front of me, but it sounds like what's being described is a non-adjustable fixed bias scheme. Mesa does it with their fixed bias amps. PITA.
     
  14. Scottgun

    Scottgun

    Jan 24, 2004
    South Carolina
    It's fine if the amp was designed for it.
     
  15. Desigined in what way? If it's a cathode biased output section, then yes.

    If it's fixed bias (adjustable or non) then it should be checked at the very least. Otherwise, how do you know if it's operating within proper parameters?
     

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