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Kendrick Champ bias circuit

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  • #16
    It means I'm biting my lip trying not to say anything negative- in this case, anyway. A veiled Gerald Weber reference, if you will.
    Last edited by The Dude; 08-13-2020, 12:01 AM.
    "Yeah, well, you know, that's just, like, your opinion, man."

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    • #17
      Originally posted by Helmholtz View Post
      Sorry to ask, but what is the meaning of this taped mouth icon ? Tried to google it without success.
      I think it basically means "Better not to say anything because it would surely offend someone." while at the same time implying that YES, you went there without openly admitting it
      "Take two placebos, works twice as well." Enzo

      "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

      "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

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      • #18
        I guess it’s akin to the saying ‘if you can’t say something nice / positive, don’t say anything’.
        So if you’re bursting to contribute a ‘less than positive’ response, a taped up mouth may be necessary to comply with that
        My band:- http://www.youtube.com/user/RedwingBand

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        • #19
          There was one particular Guitar Show where Gerald was bragging (as he is prone to do) that you could stick anything in his Champ from a 6V6 to a 6550 and it worked just fine. No mention was made of adjusting the bias.
          WARNING! Musical Instrument amplifiers contain lethal voltages and can retain them even when unplugged. Refer service to qualified personnel.
          REMEMBER: Everybody knows that smokin' ain't allowed in school !

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          • #20
            Originally posted by loudthud View Post
            .... you could stick anything in his Champ from a 6V6 to a 6550 and it worked just fine. No mention was made of adjusting the bias.
            I recall the THD Univalve and Bivalve made similar claims - in fact they were marketed on the basis that almost any tubes could be used safely.
            I still have my Uni. I used a 6550 and a KT88 in there for quite a while. I used a whole suite of different tubes in that amp.
            It's just a simple cathode biased (bypassed) circuit with a bit beefier OT and PT (compared to the Champ).
            My point is that it's not an unreasonable claim if the components are chosen accordingly. Perhaps Gerald used oversized PT/OT iron.
            I'll accept that bias may not be optimal (centered) for all tubes, but the amp works and sounds pretty good over the 10+ yrs I've had it.
            Old Tele man: Equations provide theoretical values, SPICE provides approximate values; but, the ears provide exact values.
            Hofstadter's Law: It always takes longer than you expect, even when you take into account Hofstadter's Law.

            https://sites.google.com/site/stringsandfrets/

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            • #21
              It is just a guitar amp. FOlks often have the idea that bias is a super critical adjustment, but all you need to do is use a transformer good for the highest current, and a cathode resistor that is average for the range of tubes. SO some tubes run fairly hot and others fairly cold. They will all survive.
              Education is what you're left with after you have forgotten what you have learned.

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              • #22
                Originally posted by Enzo View Post
                It is just a guitar amp. FOlks often have the idea that bias is a super critical adjustment, but all you need to do is use a transformer good for the highest current, and a cathode resistor that is average for the range of tubes. SO some tubes run fairly hot and others fairly cold. They will all survive.
                I just wonder how that became a selling point. Anyone with some experience knows that there's an ideal bias point for a given tube type in a given circuit. It's the totally layman "tube rollers" that are attracted to such claims. This bodes poorly for the marketers of these products. They're selling the opportunity for the "tone" of different tubes without the possibility of actually realizing it. So now it's just a gimmick.
                "Take two placebos, works twice as well." Enzo

                "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

                "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

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                • #23
                  And the tube rollers are typically the guys who want to nitpick over the tiniest subtleties of the sound. So for them, it's kind of funny to tolerate a compromise 'one size fits all' approach to the bias point.
                  "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

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                  • #24
                    Originally posted by Dave H View Post

                    Cathode bias could also be made adjustable as below.

                    Click image for larger version Name:	adj CB.png Views:	4 Size:	10.0 KB ID:	910628
                    Dude, I dig this idea. This is a clever way of doing it sans negative supply. I wish I'd thought of it
                    If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

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                    • #25
                      The problem as I see it is this: all these ideas like "optimal" are really part of the hifi world. SO a circuit is not optimal for a 6L6 when you cram a 6V6 into it or whatever, yet you may find it agreeable. The music world is full of stories like the guy who poked pencil holes all over his speaker cone to get a sound he liked. HArdly optimal. SOmeone decided on 70% at some point, yet Fender never launched tham that hot. And anyone working on 5150s knows that 15ma is common - 7 watts - at idle current.
                      I can line up a dozen octal power tubes, and try them out in the little amp. Maybe we don't get all the nuance, but we do get to hear differences where all the rest of the circuit is the same. SOmeone will find that appealing.
                      Education is what you're left with after you have forgotten what you have learned.

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                      • #26
                        ^^^^^^^ If it sounds good and doesn't blow up, it's perfect.

                        Let's also be fair about the marketing in this business. Music companies need to sell gear so they all say and do whatever it takes to make the sale. If they're successful in the long run, it's probably not because of what they said to make the sale, but because their products sound good and hold up. I'd give anyone who can stay in this business for 10-20 yrs a lot of credit for that.
                        Old Tele man: Equations provide theoretical values, SPICE provides approximate values; but, the ears provide exact values.
                        Hofstadter's Law: It always takes longer than you expect, even when you take into account Hofstadter's Law.

                        https://sites.google.com/site/stringsandfrets/

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                        • #27
                          Originally posted by SoulFetish View Post
                          This is a clever way of doing it sans negative supply.
                          It also works fine with the 680R replaced by a zener for adjustable fixed bias.

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