New tubes for my Peavey JSX, how to bias? EL34's to 6L6's

Discussion in 'Pickups, Electronics & General Tech' started by skattabrain, Sep 20, 2006.

  1. skattabrain

    skattabrain slow and low

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    I just bought some 6L6 tubes to replace the EL34's in my JSX. Not familiar with biasing a tube amp ... are there hard and fast rules or do i need to bust out a multimeter to make the adjustment?

    Not sure if it's a switch (liek a mesa) or a POT I need to adjust. Tech's in my area want to hold the amp for over a week! It's like a 15 minute job to boot!

    I've some guys on another forum that basically are like pop them in and be done with them ... but that sounds plain wrong. Will ballparking the adjustment give me horrid results?

    I wish there was a local guy that could do this while I wait.
     
  2. noodles

    noodles Contributor

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    I'd be afraid to do it, unless you know exactly what you're doing.
     
  3. skattabrain

    skattabrain slow and low

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    i don't ... but i'd liek to learn. i guess i need this socket that plugs into a tube jack, then the tube over it ... then this connects to a multimeter where i measure the current.

    i'm hoping there is a trick to this to make this easy.

    you mesa guys have it easy ... pop 'em in ... flip the switch.
     
  4. noodles

    noodles Contributor

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    Well, us Mesa guys have it easy because we have to use tubes that are already within the specs of the amp. I can't just buy any old set of power tubes off the 'net.
     
  5. Jerich

    Jerich Contributor

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    NO WAY!!!!!!!!! you need to break tubes in like a Motor with new pistons/ring you need to heat up and cool down a few times doing a few bias tests to match the out put of each tube. also check the serial number of that JSX there are a few peavey XXX/JSX/5150 that have


    http://www.eurotubes.com/euro-ka.htm

    I do alot of amp repair you need an O-scope and Bias tools to be good at it...A good tube plate match will make your amp sound better and last longer it is not a Joke it gets your moneys worth also finds defective parts in your amp for the future. Most amp repairs are not authorized repair men so it takes for ever to get parts and peavey and mesa are the worste for PARTS!!!! take it to a professional ...you would never go to a Car repair for a cold would you?
     
  6. skattabrain

    skattabrain slow and low

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    yeah ... bob at eurotubes seemed to think it not a big deal ... but tops it's an hour work ... taking it apart ... warming it up ... the tubes ar e a matched quad ... he says you jsut need to check one tube ... the rest follow suit.

    i dunno ... a week???
     
  7. darren

    darren Decibel Guitars Forum MVP

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    Well, a week assumes that they've already got a backlog of work in their shop. It's not like they're just sitting around waiting for you to bring your amp in. Based on my experience with just opening up my power amp and swapping the tubes (with no biasing) i'd guess it's probably an hour of work.
     
  8. Elysian

    Elysian Banned

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    i would have a shop do it, i've done it on my blue voodoo, but it doesn't get easier than that amp, its just a simple knob with 2 leads on it for hooking the multimeter to...
     
  9. skattabrain

    skattabrain slow and low

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    yeah, but it'd be nice if they said ... bring it down friday and pick it up saturday ... versus we'll do it sometime in 2 weeks ... bring it down now
     
  10. 7StringofAblicK

    7StringofAblicK Contributor

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    I thought those were self biasing? On my XXX i just plugged the new tubes in and made sure it was set to 6l6's. Sounded amazing (much better than the sovteks) right off the bat. I've not tried it with any other amp though so...
     

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