Tube DIY Asylum

• Strange, I get different results - Ray Moth 04:02:50 03/07/07 (4)
  In Reply to: To say it another way....... posted by Tre' on March 6, 2007 at 21:07:21:

  Just modeling a pair of EL34 in pentode mode AB1 PP with quiescent cathode current (plate + screen) set to 45mA and fixed bias, the combined plate current measures 80mA at zero signal and 250mA at max. signal.
  
  

  ---

  • Ray, take a look at this - Tre' 08:06:19 03/07/07 (2)
    In Reply to: Strange, I get different results posted by Ray Moth on March 7, 2007 at 04:02:50:

    I underlined the idle current for one tube 48.7ma. and the total idle current 97.4ma. Also the max current for one tube 249ma.

    The tubes never cutoff completely. This is do to non-linearities in the tube. Min current is 21.9ma. So that current has to be added to the 249ma. So the max total is 270.9ma.

    In the graph the one axes is time and the other is current. There is never more than 270.9ma. of current being drawn at any on time. There are two points in time, per cycle, where the current draw is 270.9ma.

    (This is only a close apx, you can see that the small current really goes up a little from 21.9ma just as the other tube is reaching max (249ma.)

    Peace, Tre'

    P.S. The fact that the tubes never reach full cutoff is used by some manufactures to make Pure Class A claims for amplifiers that are really Class A/B. But that's a whole other story.
    Have Fun and Enjoy the Music
    "Still Working the Problem"
    

    • TubeCad screen shots   (Open in New Window)

    
    

    ---

    • Re: Ray, take a look at this - Ray Moth 12:37:42 03/07/07 (1)
      In Reply to: Ray, take a look at this posted by Tre' on March 7, 2007 at 08:06:19:

      I see what you mean. I was aware of the danger of confusing amplitude with RMS, when calculating plate current with signal applied. For that reason, using LTSpice, I measured the RMS current flowing through the voltage source that feeds the OPT center tap. This was during maximum signal, at 1kHz, averaged over a time period of 200ms, and I got a figure of 250mA (this excludes the screens, which are fed from a separate voltage source).

      I now doubt that the figure LTSpice gave me was, in fact, the correct RMS current. Either the simulator is wrong, or I misinterpreted it. From your example, the RMS plate current over the two tubes at max. output is ~175mA.

      Thank you for putting me straight!
      
      

      ---

      • You're welcome......(nt) - Tre' 14:42:49 03/07/07 (0)
        In Reply to: Re: Ray, take a look at this posted by Ray Moth on March 7, 2007 at 12:37:42:

        .
        Have Fun and Enjoy the Music
        "Still Working the Problem"
        
        

        ---
  • Re: Strange, I get different results - Tre' 07:38:52 03/07/07 (0)
    In Reply to: Strange, I get different results posted by Ray Moth on March 7, 2007 at 04:02:50:

    
    OK, I'm looking at a set of EL34 pentode plate curves right now and the max current at the min plate voltage (100), at 0 VDC on grid, right at max plate dissipation is 250ma.

    100V times 250ma. = 25watts plate dissipation.

    My point is if the max current draw for one tube is 250ma. then that's the max draw on the supply. Not 250ma. times two. When the one tube is at 250ma. the other tube is cutoff.

    
    Tre'

    
    
    Have Fun and Enjoy the Music
    "Still Working the Problem"
    
    

    ---

This post is made possible by the generous support of people like you and our sponsors:

Schiit Audio

---

[ Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2024, Audio Asylum, all rights reserved ]

---

[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]

---