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Svetlana 6L6 Bias BDRI

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  • #16
    Re: Svetlana 6L6 Bias BDRI

    Originally posted by Lake Placid Blues View Post
    Don't scare the OP. 30 ma per tube is only 60% if the tubes are 5881s and the plate voltage is as high as 455. If the tubes are 6L6GC then it's less than 50% plate dissipation, even at 455 plate volts. That's pretty cold. But the tubes are more likely to last past the warranty. As the current increases the plate voltage will drop some too.
    I agree. I was referencing the video I posted as well as the forum link. 30mA/side is definitely a safe albeit possibly cold bias.
    I say possibly because some amps (like my quickrod ) actually sound better with a colder bias and because according to the forum post 30/side (60) is factory recommendation.
    I think somewhere between my suggestion and your suggestion is probably perfect for the amp.


    But yes....letís help the op and not be harsh. This is how we learn.

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    • #17
      Re: Svetlana 6L6 Bias BDRI

      The bias at 92ma does seem quite high at 46ma per tube. Although lake placid did do the research and you confirm this to be fine. I appreciate that. I’m going to drop it down to 64ma to 80ma altogether ( so 32ma to 40ma per tube) and see what sounds the best to my ear. I’d rather be safe than sorry. I’ll take it in to get it properly diagnosed. I need to find a tech here in the city (Ottawa).

      Lake placid and minion. You both share the same picture. Appears to be Duane allman and Clapton? Very cool. The recorded sessions they did are on YouTube by the way. Which you likely already knew or you have vinyl. In which case I’m very jealous of that lol. Anyways, thanks for helpin me out. Special thanks,

      Jr
      The two greatest guitarists are American. The greatest Rock band is British. The greatest songwriter is Canadian.

      We are all connected. Peace n Love

      Comment


      • #18
        Re: Svetlana 6L6 Bias BDRI

        Originally posted by Jon Barr View Post
        The bias at 92ma does seem quite high at 46ma per tube. Although lake placid did do the research and you confirm this to be fine. I appreciate that. I’m going to drop it down to 64ma to 80ma altogether ( so 32ma to 40ma per tube) and see what sounds the best to my ear. I’d rather be safe than sorry. I’ll take it in to get it properly diagnosed. I need to find a tech here in the city (Ottawa).

        Lake placid and minion. You both share the same picture. Appears to be Duane allman and Clapton? Very cool. The recorded sessions they did are on YouTube by the way. Which you likely already knew or you have vinyl. In which case I’m very jealous of that lol. Anyways, thanks for helpin me out. Special thanks,

        Jr
        Yep, I'm a ABB fan boy. love em. All eras.

        This is the reason knowing your plate voltage is helpful.

        If it's 455 then the math is:

        30 (watts plate dissipation of 6L6GC)/455 = 66ma (100% plate dissipation current.) 46 ma = 70% plate dissipation. 70% is considered the high end of safe and many like it there. Therefore many techs set it there.

        If it's 475 volts however:

        30/475 = 63ma. 46 ma = 73% PD. It might not be red plating but it is getting beyond the safe zone. It might have shrill highs and muddy lows too.

        If it is 410 volts as reported in some articles:

        30/410 = 73 ma. 46 ma = 63% PD

        Comment


        • #19
          Re: Svetlana 6L6 Bias BDRI

          Does anyone still make a 6L6/6L6G/6L6GB anymore? I think those were all 20 - 25 watt tubes (or thereabouts, depending on the suffix) with max plate voltage ratings of 350-400V or so (again, depending on the suffix letters). The 6L6GC is rated for 500V on the plates and a max dissipation of 30 watts. I thought that I read that all current production 6L6's were 6L6GC's regardless of the suffix letter they tag on the end. But I could be wrong. That said, Fenders recommended 30ma per tube (60ma total) may be an attempt to more approximate the tone of the original BD's. Or, it may be a way to add some longevity to the tubes. Or, maybe a bit of both. Just a guess.

          I would experiment with the bias. The amp may sound better with a colder bias. Or not.

          Comment


          • #20
            Re: Svetlana 6L6 Bias BDRI

            Safe to say if I’m in the low 40ma per tube I should be safe. That’s good to know. Do the humbuckers push the power tubes harder than single coil?

            Yes the allmans are a favourite of mine too. What’s not to love about em. The good old boys from down south, straight rock n rollers with country and jazz influences. Likely get in sh!t for sharing this, seeing as it’s off topic but ABB songs that stand out to me.

            “Dreams” with the organ (Leslie) opener off the flrst album
            “High Falls” - 11 minute instrumental by Dickey off Win,lose,draw
            “No one left to run with” - where it all begins album

            Marshall tucker band too!

            Peace
            The two greatest guitarists are American. The greatest Rock band is British. The greatest songwriter is Canadian.

            We are all connected. Peace n Love

            Comment


            • #21
              Re: Svetlana 6L6 Bias BDRI

              Originally posted by Lake Placid Blues View Post
              Yep, I'm a ABB fan boy. love em. All eras.

              This is the reason knowing your plate voltage is helpful.

              If it's 455 then the math is:

              30 (watts plate dissipation of 6L6GC)/455 = 66ma (100% plate dissipation current.) 46 ma = 70% plate dissipation. 70% is considered the high end of safe and many like it there. Therefore many techs set it there.

              If it's 475 volts however:

              30/475 = 63ma. 46 ma = 73% PD. It might not be red plating but it is getting beyond the safe zone. It might have shrill highs and muddy lows too.

              If it is 410 volts as reported in some articles:

              30/410 = 73 ma. 46 ma = 63% PD


              You're just guessing his PV. Plus he said his tubes were "orange". Tubes properly biased @ 70% idle are not "orange". The plates should be nothing but the color of the metal grey or black. We can guess all day long what his bias "should be" but until someone sticks a meter on it we will never know. This thread is pointless.

              Bias for an amp is set in relation to plate voltage & the wattage of the tube via a mathematical formula. There is no guess work or hypothesis involved.

              Comment


              • #22
                Re: Svetlana 6L6 Bias BDRI

                I told him he needs to know the plate voltage of his amp, and provided examples why. I did not guess the plate voltage of his amp.

                Comment

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