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Pictorial of Biasing a Marshall Jubilee.

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  • #16
    Re: Pictorial of Biasing a Marshall Jubilee.

    Originally posted by J Moose View Post
    How do you set the volt meter up? Auto-ranging? DC current?
    Set it to DC Amps. The Auto Range means that the meter will change the metric range automatically. On cheaper meters, if the correct range isn't selected and the amperage exceeds that range, the fuse will blow.
    Originally posted by Boogie Bill
    I've got 60 guitars...but 49 trumpets is just...INSANITY! WTF!

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    • #17
      Re: Pictorial of Biasing a Marshall Jubilee.

      I'd be too scared of ****ing up and dying, but that is a great post Joe! Definitely vault-worthy.

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      • #18
        Re: Pictorial of Biasing a Marshall Jubilee.

        Originally posted by Christobevii3 View Post
        What do you do if an amp doesn't have a bias pot?
        Nuttin'.


        Really...if the amp doesn't have a bias pot then it's a 'fixed' or otherwise self-adjusting bias. At that point, changing a tube is no different then changing a lightbulb.



        Joe ~ What kinda volume were you running that thing at while biasing? I always thought tech's did that with no signal running through, or at least having the amp on standby...but that wouldn't apply full current to the plates would it?
        J. 'Moose' Kahrs
        mixer|producer|recordist
        mooseaudio.bandcamp.com

        Originally posted by the guy who invented fire
        All you need to make a record is a mic, some tape and maybe some bad reverb...

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        • #19
          Re: Pictorial of Biasing a Marshall Jubilee.

          Originally posted by J Moose View Post
          Joe ~ What kinda volume were you running that thing at while biasing? I always thought tech's did that with no signal running through, or at least having the amp on standby...but that wouldn't apply full current to the plates would it?
          The amp has to be running to get a reading on the amp meter, but the volume level doesn't seem to change it very much. Ideally, it's nice to have it running at stage volume, when biasing by ear, so you can hear the tightness of the low end thump, which is what I aim for. It's hard to have the guitar strapped on while doing this, so I usually just lean it right next to where I'm working, and pluck the A/D or D/G, and listen while I'm tweaking the pot.

          Here's one thing to know. You never want to turn the bias pot drastically, because it can destabilize the circuit, and you'll get erradic readings on the meter. If the numbers start jumping around, you're better off turning the amp off for 15 minutes and letting the tubes cool, then starting again later.
          Another technique is setting it at 35, play and listen, 36, play and listen, 37, play and listen etc. The main point of biasing is to get the amp sounding as healthy as possible, and sometimes it's hard to tell when you're just fiddling with the bias pot and whacking the strings on the guitar.

          The most important thing, besides NOT electrocuting yourself, is NOT overheating the tubes. If you ever go past the desired numbers, you could fry your tubes. You'll know you're doing the wrong thing if the plates start turning orange. This is why it's not a good idea to do this without a meter on it. At least you know if you're in the ballpark then.
          Originally posted by Boogie Bill
          I've got 60 guitars...but 49 trumpets is just...INSANITY! WTF!

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          • #20
            Re: Pictorial of Biasing a Marshall Jubilee.

            great thread!
            Marshall 2555
            Marshall 2203 Caswell Mod
            '05 Gibson Les paul standard faded
            '78 Gibson Les paul standard
            Martin Acoustics
            Duncan pickups
            Marshall Greenback cabs

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            • #21
              Re: Pictorial of Biasing a Marshall Jubilee.

              Hoffman Amps sells the parts and has instructions for making your own bias current checker.

              Here's an interesting and off-the-beaten-path explanation of biasing an amp from the Tone Lizard. Don't have an oscilloscope yet though...

              Chip
              Heritage 535 Special, Warmoth frankenstrat, MIM Strat, & Taylor 314C(no E)
              Amp Builds: Tweed Princeton (5F2-A) variation, 2 BF Princeton Reverb clones, & Super Reverb clone
              Sometimes use a Blues Jr., Tech 21 Trademark 10 & Power Engine 60
              SPG modded DS-1, TS-7 & CryBaby; Visual Sounds Rte. 66 & H2O; Guyatone Tremolo
              SD pickups: SSL-2, APS-2, tapped Quarter Pound, Custom 5 & Antiquity humbuckers

              "Conan! What are the best things in life?"
              "Girls, guitars, guns and cars!"

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              • #22
                Re: Pictorial of Biasing a Marshall Jubilee.

                +1 to all, Very Informative, Deffinatly Vault Worthy

                ~Mitch~
                Buy My Neck!!!

                Stage3-1

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                • #23
                  Re: Pictorial of Biasing a Marshall Jubilee.

                  shameless bump.

                  this thing NEEDS to be in the vault.

                  someone like me, who is just getting into tube amps, this thread is very valuable.

                  Thanks Jonesy
                  -Greg

                  Guitars:
                  2016 Ibanez RG6003FM (JB/'59nJ)
                  2018 G&L Tribute Legacy (Hot Rails/stock/stock)
                  2019 Squier Affinity Telecaster HH (Esquire'd w/ JB)
                  Applause/Ovation AE28 Acoustic/Electric

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                  • #24
                    Re: Pictorial of Biasing a Marshall Jubilee.

                    do you just use a single bias probe on one tube or do you test on both? Im new to this but am keeping up so I can do it myself.

                    Thanks
                    Originally posted by ratherdashing
                    As long as Giada exists, there is no reason for Rachel Ray.
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                    • #25
                      Re: Pictorial of Biasing a Marshall Jubilee.

                      Originally posted by skyydogg01 View Post
                      shameless bump.

                      this thing NEEDS to be in the vault.

                      someone like me, who is just getting into tube amps, this thread is very valuable.

                      Thanks Jonesy
                      As far as I know, the Blues Jr. (which should be there soon) is fixed bias. Don't hold me to that, but I believe it is.

                      But this is still all greek to me, and all but one of my amps have been tubers.

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                      • #26
                        Re: Pictorial of Biasing a Marshall Jubilee.

                        Vault Worthy! Great info!

                        I would like to add a measure of safety by suggesting fiberglass screwdrivers be used in "live" chassis. A metal tool shaft can fry an amp or cause injury as was already noted!

                        "Fiberglass screwdrivers" are the safest way to turn the trim pots. They are really inexpensive too! Many use the smallest amount of metal in the just the tip.

                        http://www.tecratools.com/pages/datacom/alignment.html
                        Last edited by Sludgenutz; 02-15-2007, 09:23 PM.

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                        • #27
                          Re: Pictorial of Biasing a Marshall Jubilee.

                          Originally posted by bigalthethird View Post
                          As far as I know, the Blues Jr. (which should be there soon) is fixed bias. Don't hold me to that, but I believe it is.

                          But this is still all greek to me, and all but one of my amps have been tubers.
                          yeah, it's fixed bias. Just more info that i'd like to know if I decide to do the "variable bias" mod.
                          -Greg

                          Guitars:
                          2016 Ibanez RG6003FM (JB/'59nJ)
                          2018 G&L Tribute Legacy (Hot Rails/stock/stock)
                          2019 Squier Affinity Telecaster HH (Esquire'd w/ JB)
                          Applause/Ovation AE28 Acoustic/Electric

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                          • #28
                            Re: Pictorial of Biasing a Marshall Jubilee.

                            I stopped biasing my amps after being shocked once.... ONCE

                            My left arm felt like it was zapped by lighting and was a dull numb appurtance to my body for about one hour.


                            HURTS!
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                            • #29
                              Re: Pictorial of Biasing a Marshall Jubilee.

                              Originally posted by Stratman View Post
                              I stopped biasing my amps after being shocked once.... ONCE

                              My left arm felt like it was zapped by lighting and was a dull numb appurtance to my body for about one hour.


                              HURTS!
                              You did touch something on the amp..or did you use a non-plastic screwdriver?
                              Originally posted by Guitarist
                              Honestly, I like Scott's words. "There is a rhythm to life. Ride the waves."

                              And keep in mind that while nothing lasts forever, nothing is lost.
                              http://soundcloud.com/adrian-czarnecki/tracks

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                              • #30
                                Re: Pictorial of Biasing a Marshall Jubilee.

                                Cool post Joe
                                And one very nice amp I might add!
                                Hehe have been zapped a few times as well....me not like high voltage very much...lol

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