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5881's in SG Systems SG-215?

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  • #1

    5881's in SG Systems SG-215?

    Whoah! What a beast!
    CMI Electronics SG Systems SG-215, supposedly by Gibson, this is the massive bass version.

    SS preamp and tube power amps, with a pair of 8417's.

    Aside from replacing bad filter caps, it had a fried screen resistor and blew the on board 1/2 amp fuse.

    I don't trust the output tube that had the fried screen grid resistor, the current draw is pretty high when pushed.

    Some have recommended 6550's or EL34's as replacements.
    What do you think about running EH 5881's?
    They're pretty robust and the amp is like a Music Man, with around 640 volts on the plates and half on the screens.
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  • #2
    Originally posted by drewl View Post
    Whoah! What a beast!
    CMI Electronics SG Systems SG-215, supposedly by Gibson, this is the massive bass version.

    SS preamp and tube power amps, with a pair of 8417's.

    Aside from replacing bad filter caps, it had a fried screen resistor and blew the on board 1/2 amp fuse.

    I don't trust the output tube that had the fried screen grid resistor, the current draw is pretty high when pushed.

    Some have recommended 6550's or EL34's as replacements.
    What do you think about running EH 5881's?
    They're pretty robust and the amp is like a Music Man, with around 640 volts on the plates and half on the screens.
    With that high voltage, might try KT88 or 6CA7. And don't expect 100 watts. It will be plenty loud, don't worry about that.
    This isn't the future I signed up for.

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    • #3
      I'm getting 150w into an 8ohm test load!

      Comment

      • #4
        Originally posted by drewl View Post
        I'm getting 150w into an 8ohm test load!
        At clip or full out square wavin'?

        Either way, I have an SG Systems 2x12 combo I've been using for a mini desk several years. You're inspiring me to fix it up. Some lucky guitarist ought to love this thing.
        This isn't the future I signed up for.

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        • #5
          I had an SG Systems SG-115 in the shop a while back. We were joking about the giant oven knobs on the thing. When the customer came to pick it up, I set a couple of burners from a stove on top of it.
          "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

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          • #6
            I wouldgo with SOVTEK 5881WXTs. The famous ones, with oval holes in the plates. They go in Ampegs all day; I hadput a pair in a VT-40 and tested it at "full-tilt whackage" for about 2 hours. Just bias them a little cooler than "the usual" 70% & they will probably be okay.

            Those 5881WXTs are NOT a vintage-style 5881. They're closer to a 6L6GC, but on steroids.

            Justin
            "Wow it's red! That doesn't look like the standard Marshall red. It's more like hooker lipstick/clown nose/poodle pecker red." - Chuck H. -
            "Of course that means playing **LOUD** , best but useless solution to modern sissy snowflake players." - J.M. Fahey -
            "All I ever managed to do with that amp was... kill small rodents within a 50 yard radius of my practice building." - Tone Meister -

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            • #7
              That's what everyone says about the 5881's.

              VT40? Nice!
              I had one and it just screamed "Can't you hear me knockin' "

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              • #8
                Just the WXTs. I don't accept substitutes.

                Justin
                "Wow it's red! That doesn't look like the standard Marshall red. It's more like hooker lipstick/clown nose/poodle pecker red." - Chuck H. -
                "Of course that means playing **LOUD** , best but useless solution to modern sissy snowflake players." - J.M. Fahey -
                "All I ever managed to do with that amp was... kill small rodents within a 50 yard radius of my practice building." - Tone Meister -

                Comment

                • #9
                  Originally posted by Justin Thomas View Post
                  Those 5881WXTs are NOT a vintage-style 5881. They're closer to a 6L6GC, but on steroids.

                  Justin
                  Sorry to nitpick but 5881 definitely has a rep for not failing. However it is a weaker tube than 6L6GC (in regards to power output, not failure rate). In my experience a 100W fender puts out 100-105W with 6l6GC and usually about 85W with Sovtek 5881.

                  Do you bias it according to 23W max plate dissipation? I think that's what you're supposed to do but not 100% sure since I don't use those tubes.

                  Edit: or maybe I am wrong. I could see how it would be a really good tube for V4/VT22 since that amp is pretty punishing on the power tubes. I feel like your average V4 with ~535V plate voltage does about 105-110W at clipping with JJ 6L6GC. What does a 5881 do in that circuit?
                  Last edited by nsubulysses; 09-12-2018, 03:38 PM.

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                  • #10
                    I'm not that worried about the output power. I use them because they don't blow up in torture chamber amps. I bias them according to 6L6GC spec not 5881 spec. I'm not really that scientific about it. I've never had anyonecsay their amp wasn't loud enough after being fitted with them. What I have heard is they dont need new tubes after a couple weeks or gigs where their other tubes crapped out in no time.

                    Justin
                    "Wow it's red! That doesn't look like the standard Marshall red. It's more like hooker lipstick/clown nose/poodle pecker red." - Chuck H. -
                    "Of course that means playing **LOUD** , best but useless solution to modern sissy snowflake players." - J.M. Fahey -
                    "All I ever managed to do with that amp was... kill small rodents within a 50 yard radius of my practice building." - Tone Meister -

                    Comment

                    • #11
                      And most 5881 are current production, which are really just 6L6. Unless you are using ancient NOS 5881.


                      None of those hold a candle to the original 8417.
                      Education is what you're left with after you have forgotten what you have learned.

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                      • #12
                        You sure are right.
                        I have a quad in a little old Bogen 100 watt power amp that just screams!

                        Comment

                        • #13
                          Originally posted by Enzo View Post
                          And most 5881 are current production, which are really just 6L6. Unless you are using ancient NOS 5881.
                          Just to make things even more difficult, there are now current production 5881 re-issues (like new tung-sol brand) that are original spec. 23W tube with the lower voltage ratings. The ad copy often cautions against using them in 6L6 circuits.
                          Originally posted by Enzo
                          I have a sign in my shop that says, "Never think up reasons not to check something."


                          ​

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                          • #14
                            For 5881's I'd have to increase the bias supply, and it wasn't putting out near as much power.
                            The 6550's I have are wide base and don't sit in the sockets right since they hang upside down.

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