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  • #1

    New to tubes, please help

    Hi all, so I am new to tube amps, so was wondering what will happen in the following scenario:

    My amp has 3 - 12AX7 preamp tubes and 2 - EL34EH power tubes. What would happen to the amp if one of the pre-amp 12AX7 tubes stop working? (IE: it doesn't light up) If one goes bad, do they all need to be replaced with the same brand/type?


    Thanks

    (I am wondering if this may be related to my previous post regarding the level knob not working on one of the channels found here: http://www.jcfonline.com/threads/108...annel-easy-fix )
    Last edited by stevoc; 07-13-2010, 04:41 PM.
    "Some days you're the dog, other days you're the hydrant." - on the back of the business card for Bella the Pomeranian

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  • #2
    No. You can mix and match and shouldn't have any problems.
    "It's hard to be enigmatic if you have to go around explaining yourself all the time"

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    • #3
      Originally posted by marcus View Post
      No. You can mix and match and shouldn't have any problems.


      Will the amp stop working if one tube fails?
      "Some days you're the dog, other days you're the hydrant." - on the back of the business card for Bella the Pomeranian

      The comments expressed here do not necessarily reflect the opinions of management.

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      • #4
        Yep, just get a new one and pop it in there. Different ones will change the tone of the amp, you can swap them around and stuff.

        It's kind of unusual for a preamp tube to fail, though.

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        • #5
          Originally posted by stevoc View Post
          Will the amp stop working if one tube fails?
          It depends on what the tube is doing, but probably it will.
          "It's hard to be enigmatic if you have to go around explaining yourself all the time"

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          • #6
            Originally posted by MakeAJazzNoiseHere View Post
            Yep, just get a new one and pop it in there. Different ones will change the tone of the amp, you can swap them around and stuff.

            It's kind of unusual for a preamp tube to fail, though.

            I'm guessing it was DOA. The amp still works however even though the tube doesn't light. Probably not related to my gain channel level not working though, huh?
            "Some days you're the dog, other days you're the hydrant." - on the back of the business card for Bella the Pomeranian

            The comments expressed here do not necessarily reflect the opinions of management.

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            • #7
              Are you sure it's not working? Some preamp tubes don't light very bright.
              I feel my soul go cold... only the dead are smiling.

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              • #8
                Now I'm not so sure....it may not light, but it's sure getting hot. Probably fine, you think?
                "Some days you're the dog, other days you're the hydrant." - on the back of the business card for Bella the Pomeranian

                The comments expressed here do not necessarily reflect the opinions of management.

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                • #9
                  Most likely fine.
                  I feel my soul go cold... only the dead are smiling.

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                  • #10
                    I can't see any glow from the GT 12ax7's in my blue voodoo but I know they are working.. But the JJ's in the Ultra Plus are really bright.. so... May not be an issue, but it was a new, closeout model, right? They should have the same brand tubes in it and you'd think they'd all be about the same... no? Are you sure they're all 12ax7's? Don't some amps come with a different model for something that may not glow as bright? Just some stuff to check.. I'm very certainly no expert by any means..
                    Every man dies... Not every man really lives!!

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                    • #11
                      They are 12ax7's and they are all the same brand. Thanks for the input.

                      I contacted a local authorized Randall repair shop and they can fix the level knob at no charge since it's new. So I am going to keep it and just get it fixed.
                      "Some days you're the dog, other days you're the hydrant." - on the back of the business card for Bella the Pomeranian

                      The comments expressed here do not necessarily reflect the opinions of management.

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                      • #12
                        Maybe the heater circuit isn't working in that tube? Anyway, yes replace it. I doubt it's related to the level knob, but you never know.

                        12AX7s can be used for many things. Phase inversion, gain stage, effects loops, reverb, etc. Since you state in the other thread that the gain channel doesn't get very loud, I'm guessing it's involved in a gain stage for that channel.

                        High-gain amps get most of their tone from the preamp, so read a couple reviews before replacing the tube. www.tubedepot.com and www.thetubestore.com are two places I've purchased from before.
                        Scott

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