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Guitar amp tubes?

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  • Guitar amp tubes?

    I have picked up a peavey ultra 120 (not an ultra plus 120) guitar amp and was looking at it and it has two different types of power tubes in it (2 6l6r, and 2 6l6ge). Shouldn't all the power tubes be the same? I would think they should but am not sure. It does operate and it was free so I want to use it to learn about tube amps. Also before the high voltage warnings come I already know about that and will take precautions if I get that far into it.

  • #2
    Originally posted by killa View Post
    ...Shouldn't all the power tubes be the same?,,,
    All the retube kits show all 4 of the 6L6xx being the same, usually matched.
    6L6GC is commonly used. 6L6WGB, 6L6WXT as well
    "Not a Speaker Designer - Not even on the Internet"
    "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

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    • #3
      Matched tubes are best, but not absolutely necessary. With the price of tubes being what they are a previous owner probably couldn't afford, or just didn't bother, to change all of them at the same time.
      www.billfitzmaurice.com
      www.billfitzmaurice.info/forum

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      • #4
        How much does not having matched tubes affect the performance? This particular amp has no bias adjustments so matched would probably be best as you said. There seems to be a ton of misinformation on guitar forums. Drives me crazy when people don't know how to use their gear properly. Even more so when it is a sound guy!

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        • #5
          Mu (voltage gain), Gm (transconductance) and Rp (plate resistance) are what is being matched. Under-biased tubes will wear out prematurely, overbiased contribute less to the output signal.
          Increase with odd order harmonics due to performance differences
          "Not a Speaker Designer - Not even on the Internet"
          "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

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          • #6
            Originally posted by killa View Post
            How much does not having matched tubes affect the performance?
            It won't be hi-fi. But it's a guitar amp, it's not supposed to be. Case in point: After CBS bought Fender in 1965 the amp line was re-engineered. The primary circuits weren't altered, but various 'improvements' were made, such as shielded internal wiring and SS rectifiers. Technically the amps were 'better', but the general opinion of players was that they were ruined. Even today the prices of black face versus silver face reflect that.
            As to your situation, get a schematic to determine the tube pairings. There should be two tubes paralleled on either side of the push-pull. You may find that it sounds better with one of each tube paired than having one matched pair on one side of the push-pull and one matched pair on the other.
            www.billfitzmaurice.com
            www.billfitzmaurice.info/forum

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            • #7
              If you search the net you can buy a new matched quad of JJ 6L6GC tubes for under $70.
              Craig

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              • #8
                Originally posted by PWR RYD View Post
                If you search the net you can buy a new matched quad of JJ 6L6GC tubes for under $70.
                There you go. Guys who have been working with Tubes and Transformers all their lives and been fixing guitar amps professionally, understand the rationale behind matching.
                As noted
                There seems to be a ton of misinformation on guitar forums.
                Most guitarists I've encountered don't have electronics background, or acoustics for that matter.
                Consider the Source...
                "Not a Speaker Designer - Not even on the Internet"
                "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

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                • #9
                  I went ahead and got new power tubes and for the free shipping (over 100$) I went ahead and got some new preamp tubes to try out also. Next step will be to clean the pots and look over everything while I wait. I might also recover the box since I have some duratex laying around.

                  I haven't managed to find a schematic yet but I emailed peavey and am waiting for a response.

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                  • #10
                    Peavey came through so I thought I would post for anyone interested
                    Attached Files

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                    • #11
                      Cool. Thanks!
                      Craig

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