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Maximum wattage, 2 6V6 in PP, cathode bias

Discussion in 'Amp Tech Center' started by jhawk, Sep 20, 2017.

  1. printer2

    printer2 Poster Extraordinaire

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    I was reading an interview of a guy that was a ground breaker in decoding DNA. He said he had a choice to take when he started out as a researcher. He could go into physics, which he loved, or go into decoding biology. He said all the easy stuff in physics was already taken (you needed atom smashers to test stuff) while biology you just needed to look into a microscope and could discover new things. In the early days of amplification, the general rules for tubes were mostly already thought up, Leo just packaged them well and decided output tubes did not have to last ten years.
     
  2. Old Tele man

    Old Tele man Friend of Leo's

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    Prior to my leaving USN, I had employment interviews with Fender and Tel-Ray while I was stationed at NAS Point Mugu, CA. And, although I (obviously) didn't meet or talk with either Leo or Forrest, I did meet Ed Jahns (but only very briefly) and got a "royal" tour through both the guitar and amp shops from an older gentleman from the amp shop. I asked lots of questions about Leo and my tour "guide" had lots of answers about how & why Leo did things. Ultimately, however, I did NOT get a job offer from Fender (no degree yet) but I did get one from Tel-Ray. So, when my enlistment was up, I returned home and went back to college and completed my degree using my GI Bill...10 years after graduating high school.
     
    Last edited: Sep 24, 2017
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  3. Bendyha

    Bendyha Friend of Leo's Silver Supporter

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    Wow...I'm impressed by all those people you lot get to mix with...I would have loved to chat with Ed Jahns.
    But while we are name dropping, I would like to mention my getting to shake hands with Jim Marshall once, and haveing chatted to Paul Rivera a few times at trade fairs.
    I have stood next to several big name celebs whilst urinating, but it's not always the best place to try to shake someones hand:oops:
     
  4. Silverface

    Silverface Poster Extraordinaire Platinum Supporter

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    Jeeez - you owe me for *another* t-shirt. That was a bona-fide "dual-nostril coffee ejector"!:lol:

    Part of meeting folks was from working in the industry part-time and working at NAMM, going to product launches etc. Others were from living and working in the right places at the right time. And knowing how to "look the part" , be able to ignore "authorized employees only" signs yet somehow not bother anyone (plus dumb-a** luck) helps! I'm mostly happy I about what I learned, not that meeting anyone was that big a deal.

    But my 23 year old son is the one with the craziest industry-related stories, mostly from when he was 8-11. I'll tell those somewhere here one day, they're.....bizarre!o_O
     
  5. peteb

    peteb Friend of Leo's

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    Fender lover, your a good poster, appreciate it, always.



    How can 1 volt bias amplify 20 signal volts?


    It makes no sense by normal tube rules.




    What rules are you using?
     
  6. peteb

    peteb Friend of Leo's

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    No good reason, just a hunch.


    Power is power, right?



    Is high voltage low current power just the same as low voltage high current power?






    What if they never considered 500 v on the plates when they came up with 12 or 14 watts as maximum plate dissipation for the 6v6? What if they then tried 500 volts and found it could take in 15 W per tube?


    Doubtful.



    Here's an anolgy for max power in. What ever you want to call it, the amount of power the tube can put out is limited by the amount of power the tube can take in.



    Here's an analogy with water:


    A sponge can soak up a lot of water, but once it absorbs it's full amount, it can't absorb any more.


    The power tube plate can only absorb so much power, power beyond this........






    How could someone define max plate dissipation?





    Test all possible operating conditions, find the max output power, measure the according max plate dissipation under max power out, that's it.
     
  7. Bendyha

    Bendyha Friend of Leo's Silver Supporter

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    Here we see the over dissipation of a tube sponge............... of course, this is a single-ended example, but it does have its roots in rock.

    upload_2017-9-25_12-43-27.png
     
  8. peteb

    peteb Friend of Leo's

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    I am fine leaving the bias of the cathodyne phase inverter alone.




    I just want to point out that no one is willing to try to explain how a one volt bias can be used to amplify a 20 volt signal. I dont blame anyone either. I wouldn't want to try to explain how a one volt bias could be used to amplify a 20 volt signal.
     
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  9. Bendyha

    Bendyha Friend of Leo's Silver Supporter

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    Spherical Earth

    Evolution

    Global Warming

    Floating Bias

    Okay Peteb............I'll admit it...............they are all lies.

    Thousands of electronic textbooks have got it wrong. All those lies about cathode followers.
    The proof that you alone are right, is that you have not found an explination that proves it to you in a way that makes sense to you.

    You are quite right...I don't want to explain it to you....because you know i'm wrong.

    Ohms law is a conspiracy, so are all those thermal dynamics laws. Evil laws that have been created by people trying to hide the truth from us.

    Most of the posters here are in on the joke, i'm surprised that you didn't see through it earlier....but then agian....you always did know, didn't you.

    Tide goes in and out................. upload_2017-9-25_19-19-39.jpeg ..............can't explain that !
     
    Last edited: Sep 25, 2017
  10. Old Tele man

    Old Tele man Friend of Leo's

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    This post is about "maximum-wattage-2-6v6-in-pp-cathode-bias"...so, let's KEEP it about that subject.
     
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  11. bblumentritt

    bblumentritt Tele-Afflicted Platinum Supporter

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    jhawk,

    For what I think you're looking for, there are several ways to get more headroom out of a 5E3, rather than "more watts". The problems you're experiencing are due to too much gain on the front end, too much bass response, and running the output tubes at 96% of maximum dissipation. This can be easily fixed:

    (note. All resistor, B+, and capacitor values are negotiable. Changing the value of one affect the value of the others.)
    • Cool down the distortion/gain in the front end.
      • Lose the cathode bypass cap on V2a, the driver stage, or perhaps change it to 4.7µF from 25µF.
      • Raise the supply voltage of V1 by reducing the supply dropping resistors, say from 5k to 4.7k and possibly from 22k to ~20k, dependent upon the other changes. If you lower the B+, we have to lower the dropping resistors. The idea is to increase the headroom on the preamp, and increase the dynamic response on the output section.
    • Open up the bandwidth.
      • Change the .1µF coupling caps ion the front end to .02µF. Leave the post PS coupling caps at .1µF.
    • Tighten the power supply.
      • Change the power transformer to lower voltage/more current.
      • Lose the tube rectifier and use diodes across the 5Y3 tube socket.
      • Boost the B+ caps from 16µF to 20µF.
      • Halve the bias feed resistors from 220k to 110k.
      • Change the 6V6 cathode bias resistor to a higher value, anywhere from 270Ω to 400Ω, depending up the other changes.
    Here's the net, and the why:
    1. Lower the gain on the front end by raising the supply voltage on the preamp, removing the bypass cap on the driver, and restricting the low-frequency response by changing the bypass caps. A 5E3 typically has almost twice the gain on low frequencies as it does on the highs. This provides the later stages with slightly less low frequency boost, tightens the feel of the amp, and allows for greater output stage activity. The output section has full frequency response, but the small output transformer limits saturation and low frequency response. Onset of cut-off distortion will be raised from about 2 on the Volume control to about 5.
    2. Tighten up the power supply.
    3. Allow the output tubes more dynamic range.
    What we're doing here is cooling down the front end, and opening up the power section from more output harmonics and dynamics, and a tighter feel.

    I would also decouple the 6V6 screens, and modify the ground scheme for improved durability and less noise, use shielded input cables, use a good, low noise 12AX7, such as a new production Tung-Sol, in V1, and use 1W resistors instead of 1/2 W.

    The 5E3 is a great platform; it can be made even better for modern players with a few minor design mods.
     
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  12. Commodore 64

    Commodore 64 Friend of Leo's

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    Put a large grid stopper on the PI too (merlin).
     
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  13. printer2

    printer2 Poster Extraordinaire

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    Do...........you..............talk.....like..............this.................also?


    Cathodyne splitter is just a cathode follower with the resistor split and one half on either side of the tube. As another hint, using a Mosfet as a cathode follower and it is called a source follower. Both circuits (or three?) do something, they follow. They also have 100% NFB. That should get you half way there if you think about it.


    On the power, think of how the tube limits the electrons through it, effectively it is acting as a resistor at a given point in the signal swing. But it is not a perfect device, if you can analyze how it works given its operating conditions you could figure out why it can make more power at higher voltages.
     
  14. clintj

    clintj Friend of Leo's

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    I think that loud pop you heard was a paradigm shifting without a clutch.
     
  15. peteb

    peteb Friend of Leo's

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    I don't type that way, so why would I talk that way?



    Printer2,


    I am curious what you have to say about the bias of the cathodyne phase inverter.



    It's got to amplify power tube like signal voltages, 20 volts and even more.



    There are contributing posters around the amp tech center that insist that the cath PI has a small preamp tube like bias, of one volt.


    Normally the bias voltage exceeeds the signal voltage, which is normal tube action and is easy to explain. Why do these guys insist that the signal voltage can now exceed the bias voltage by 20 to one? It makes no sense tube wise, it would be impossible to explain if you tried to use tube terminology like bias, signal, valve operation and current. So I see why no one wants to try to explain it by why do they cling to it?
     
  16. printer2

    printer2 Poster Extraordinaire

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    Your not trying hard enough.




    It does not amplify.





    It has 100% NFB, what comes in goes out.





    It follows the signal.




    Say you look at the input signal and then blink.




    In the time you look again the signal goes up 5V.




    In the time your eyes were closed the output signals changed 4.9V.



    0.1V is less than 1V bias.




    Goodnight.
     
  17. peteb

    peteb Friend of Leo's

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    This is what I mean by explaining it in tube action terminology:



    As long as the signal voltage is less than the bias voltage it's easy to see how the positive signal voltage opens up the tube by undoing the negative bias voltage, allowing more current to flow.



    If the signal voltage is much larger than the bias voltage, it would be hard to describe tube action and what it takes to open up the valve. It's the undoing of the negative bias voltage that opens up the tube.
     
  18. Cjl77

    Cjl77 Tele-Meister

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    There is no "undoing" of the bias voltage. Bias voltage is D.C. Voltage, that the AC signal voltage swings around.
     
  19. peteb

    peteb Friend of Leo's

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    The positive AC signal takes away from the negative DC bias voltage that acts to block the flow of current.

    It OK to subtract AC from DC.







    If I was to change my thinking to accept a 1 volt bias to use with a 20 volt signal I would use this reasoning.


    The cath PI is a pre amp tube and has a pre amp plate voltage so a small pre amp bias would be enough to prevent redplating.


    And it's been said that there is nothing special about a negative grid, it can go positive and continue to attract more and more electrons off the cathode as it gets more and moe positive, and get more and more electrons headed on their way to the plate.



    They do talk about being in the middle or linear part of the tube, and I wouldn't really call this being in the middle but who knows and we won't worry about that.



    One thing that might make some sense about having such a small bias for such a large signal is that the cathodyne phase inverter or the cathode follower is the one tube with no gain. Is that the connection? The small bias is the very reason that they have no gain?
     
  20. peteb

    peteb Friend of Leo's

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    My own criticism of my own argument for the 1 volt bias is that a negative grid is important.


    Without a negative grid at idle you would have automatic and immediate red plate.



    The grid can't remain positive, and with a 10 volt positive signal on the plate that's a lot of positive with very little negative to counter the flow of electrons.
     
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