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Efficiency of class A AB and B. What does it mean?

Discussion in 'Amp Tech Center' started by peteb, Jul 17, 2018.

  1. Old Tele man

    Old Tele man Friend of Leo's

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    Example of what viccortes285 describes above is:

    0W = 0A * any voltage

    9.8W = 0.025A * 400V

    As the bias is reduced, idle current increases, causing plate voltage (not B+) to be "sucked" down, ie: plate dissipation increases.
     
    Last edited: Jul 20, 2018
  2. elpico

    elpico Tele-Afflicted

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    Peteb,

    You’ve mixed up where to put that 70W number in your example. The 70W doesn’t tell you the power dissipated in the tubes, it’s the TOTAL power disipated in the speaker and tubes COMBINED. It’s the overall amount of power disipated in the system, and we’re trying to see how that power is divided between the parts in the system. That’s what efficiency means. If you had 1W in the load and the tube is also dissipating 1W then we’d say the system is 50% efficient because we have 2W TOTAL power disipation and 1W of that is making it to the speaker. 1W output / 2W total = 0.5 or 50% efficiency.

    In your example if we have 70W total in the system and 55W are being disipated in the load (speaker) then only 15W are being disipated in the amplifier (power tubes + transformer).

    70W total x 0.785 efficiency = 55W output

    70W total - 55W output = 15W wasted in the tubes

    15W disipated in 2 tubes = 7.5W per tube

    = well within their ratings and nothing “has to give”
     
    Last edited: Jul 21, 2018
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  3. peteb

    peteb Friend of Leo's

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    Elpico thanks,




    You are not saying that the tube is biased at 7.5 W are you?


    7.5/ 30 = 25% of MPD. The paper already gave the idle bias as over 70% of MPD.




    The two plates are dissipating the whole input power, 70 W. I will go along with you that the speaker is dissipating 55 W. The difference, 15 W would be energy used up in the process, this could be the wasted heat dissipation.







    These different interpretations results from different interpretations of dissipation.



    Plate dissipation, Ip*(Vp-Vc), is the input energy to the tube. It’s what gets calculated for the bias calculation. When measured at idle, it is the idle input energy, the idle plate dissipation. In class AB fixed bias, the plate dissipation increases with signal, in class AB cathode bias supposedly it decreases with signal, in class A, this plate dissipation is the same at idle and under full power.





    Then there is the other formula for dissipation.


    Power in - power out = dissipation




    Clearly these two dissipation’s cant be the same thing. To clarify, let’s call the second dissipation heat dissipation, or wasted energy, and the first one is DC energy input to the tube.












    To understand this, a ‘big picture’ understanding of dissipation is needed.





    Most people are not aware that plate dissipation gets viewed as both of these distinctly different things and that’s why there is so much confusion about plate dissipation and wasted heat energy.
     
  4. peteb

    peteb Friend of Leo's

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    To make this point clearer.



    When they say the max plate dissipation for a 6L6 tube is 30 Watts, they mean the maximum input DC energy is 30 W.



    They don’t mean that the maximum amount of wasted energy due to heat is 30 Watts.
     
  5. peteb

    peteb Friend of Leo's

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    I think the efficiency question is fairly well covered.

    Except for documented examples of class B.






    The last thing I wanted to say about efficiency.






    The plate dissipation ratings for tube types is the great leveler for tube amps.



    everyone knows what to expect from two 6L6 tubes. It doesn’t matter who designed or built the amp, everyone knows what two 6L6 tubes can do.
     
  6. elpico

    elpico Tele-Afflicted

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    Nope, this has nothing to with bias. Plate dissipation while passing signal is it’s own calculation. It is NOT the same as idle dissipation. Everyone keeps trying to communicate this to you, but you seem yo be ignoring it.

    No. that’s absolutely false.

    No they result from you not understanding how this works yet but making untrue statements about it anyways that conflict with what everyone else is trying to tell you. There are no “interpretations” of dissipation. It’s not a poem or abstract painting that’s open to interpretation. Physics has laws and facts.

    Most people aren’t “aware” of that because it’s absolute nonsense that you just made up. There are NOT two different types of dissipation. You’re very, very mixed up here. There are people here who are willing to donate their time to help you learn how this works but if you keep your ears and mind closed there’s nothing they can do for you.
     
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  7. elpico

    elpico Tele-Afflicted

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    Dead wrong. They mean the maximum amount of sustained heating the plate can survive is 30 Watts.

    You’re all tangled up in imaginary nonsense about AC vs DC but Pete, THERE’S NO SUCH THING AS “AC WATTS” OR “DC WATTS”. There’s only watts. Look up what a watt is please.
     
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  8. Bendyha

    Bendyha Friend of Leo's Silver Supporter

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    Ohm Slaw - Chopped-up electronics terminology, thrown together and mixed-up. - Highly allergenic.
     
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  9. Mexitele Blues

    Mexitele Blues Tele-Afflicted

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    Mmm. Sounds good on a class a/b push-pulled pork sandwich.
     
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  10. Old Tele man

    Old Tele man Friend of Leo's

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    Does your Deli deliver?
     
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  11. LudwigvonBirk

    LudwigvonBirk Tele-Holic

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    I am all for laws and facts, but also welcome properly supported scientific inquiry which might possibly disprove those laws or facts. To be a little more topic neutral...

    Hypothesis:

    On an lcd, as the increase of the spacing between lines of rgb 0-0-0 text displayed on an rgb 100-100-100 background expands, the distortion of the laws of physics as displayed in text will increase.
    ...
    Can anybody boil that ^ down into an equation, or cite one, that we can start with?*

    Also.

    I have not thought this all the way through. As of now, I sub-postulate that

    1) my hypothesis is not affected at all by AC-Hum.

    2) my hypothesis is not affected at all by heat.

    3) my hypothesis is not affected by time.

    4) The line-spacing-induced text distortion (of the laws and facts) may or may not be linear. [Study item]
     
    Last edited: Jul 21, 2018
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  12. LudwigvonBirk

    LudwigvonBirk Tele-Holic

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    *Draft:

    +Dtls = -Tr

    (As the distance of text line spacing increases negative truth increases)
     
    Last edited: Jul 21, 2018
  13. Old Tele man

    Old Tele man Friend of Leo's

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    ADMIN please delete this post.
     
    Last edited: Jul 22, 2018
  14. Art VanDelay

    Art VanDelay Tele-Afflicted

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    Things I've never said: "Hey this amp sound outstanding. It must be using electricity very efficiently"
     
  15. LudwigvonBirk

    LudwigvonBirk Tele-Holic

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    Headslap and rather brilliant point OTM! I was mistakenly attempting to introduce the current laws and facts of nature into the proposed draft equation (heat/change/distance/acceleration/distortion/CE-commodities etc), which was wrong, *my bad*.

    Draft2:

    +Zc = -Tr
     
  16. Old Tele man

    Old Tele man Friend of Leo's

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    ADMIN please delete this post.
     
    Last edited: Jul 22, 2018
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  17. LudwigvonBirk

    LudwigvonBirk Tele-Holic

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    Draft 3:

    -c =Delta-c
     
    Last edited: Jul 21, 2018
  18. elpico

    elpico Tele-Afflicted

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    Things you have said: This amp is heavy.

    Guess why that amp is heavy...
     
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  19. Bendyha

    Bendyha Friend of Leo's Silver Supporter

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  20. Bendyha

    Bendyha Friend of Leo's Silver Supporter

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    upload_2018-7-22_12-10-43.png
     
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