Tube DIY Asylum

• Re: 5842 - two triode sections in parallel - danlaudionut 12:24:33 10/15/06 (0)
  In Reply to: Need help with load line for input stage with transformer coupled/ phase splitter... posted by Balle Clorin on October 15, 2006 at 08:09:30:

  Balle

  5842 is a single triode not dual.

  As far as the loadline is concerned:
  The load would be the impedance between
  the plate to ground (through the IT
  and the last power supply capacitor)
  in parallel with the reflected load
  on the secondary of the IT (negligible).

  Load for the 5842 is about 4K at 20Hz.
  with Zo = 2 * Pi * 20Hz * 33H = 4146
  Plus trannie losses and PS cap impedance.
  Definitely not horizontal though.

  DanL
  
  
  
  

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• that load line will be nearly horizontal.... - Jim Doyle 09:26:39 10/15/06 (9)
  In Reply to: Need help with load line for input stage with transformer coupled/ phase splitter... posted by Balle Clorin on October 15, 2006 at 08:09:30:

  You should build one of these BTW.... We did it with DHTs (6B4) a
  year ago and the results were exceptionally. You can also use KT66s.

  The transformer will reflect n^2 (n=turns ratio) of the impedance on the secondary winding. In that case, the plate the of the 5842 is
  seeing 4 * (Zgrid / 2). Probably about 1 Mohm or so. For the 5842, Rp=1500 ohms. So, the slope of the loadline is going to be 1500/1Mohms which is pretty much zero slope as far as the eyeball is concerned. :)

  Unlike output transformers, which drive a low impedance, interstage
  transformers are driving the very high impendance of the grids of the next stage, so when designing with interstage transformers, just draw a horizontal line across youre plate curves and pick a idle point of (Va,Ik) such that Ik == design Ia for the the transformer specs.

  -- Jim

  
  
  

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  • Many thanks :) - Balle Clorin 09:48:24 10/15/06 (2)
    In Reply to: that load line will be nearly horizontal.... posted by Jim Doyle on October 15, 2006 at 09:26:39:

    

    My appetite for building this just increased even more..
    I will try with higher B+(420 instead of 320) to get the true 20W output, I do not understand how 320V can give 20W output power.

    Best regards
    Balle
    
    

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    • I think the 20W is from Class AB1 operation - Jim Doyle 12:12:52 10/15/06 (1)
      In Reply to: Many thanks :) posted by Balle Clorin on October 15, 2006 at 09:48:24:

      The Class A operating point ends probably somewhere around 13W or so and the next 7W are gleaned from entry into B1 mode. I'd have to run
      the calcs to see, but that's my guess. Nonetheless, those first 10W of Class A PP are indeed exquisite and plenty of power to work with.

      In this design, you are asking ALOT of the driver tube... The driver
      tube has to drive the quadrupled miller capacitance of KT88 plus the stray capacitances in the transformer. On top of that, you need all
      the voltage swing you can get - and you are getting it by a 2:1 stepup. The upside is you dont need a preamp... :) Do it passive
      on the input tube like the schematic and drive it right from your digital source.

      There are other tubes out there that will do the job... The EC8010,
      the E810F (7788), the 6C45. You might also look at Pete Millet's
      work on Triode-Strapped pentodes as drivers.

      -- Jim

      
      
      

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      • have a nice preamp thet i would liketo use ... - Balle Clorin 07:41:22 10/17/06 (0)
        In Reply to: I think the 20W is from Class AB1 operation posted by Jim Doyle on October 15, 2006 at 12:12:52:

        Many thanks for the advices.
        I doo have a nive premap so input level is not a issue. So maybe a input tube with less gain should be preferred..
        Or should the design be different in that case.

        Sorry for all the questions, I am new to this
        Best regards
        Balle

        
        
        

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  • Re: that load line will be nearly horizontal.... - mqracing 09:43:04 10/15/06 (4)
    In Reply to: that load line will be nearly horizontal.... posted by Jim Doyle on October 15, 2006 at 09:26:39:

    Hi Jim:

    I think your oversimplyfying this a bit. The reflected impedance is going to be in parallel with the inductive reactance of the transformer.
    The effective loadline will be the resultant paralleled impedance of these two factors (excluding copper and core losses from the equation).

    Since the inductive reactance will likely dominate in the case you illustrate... actually what you will have is a varying loadline with frequency. And it can never be a larger loadline than the smaller value of the two paralleled impedances. And you should also account for the phase angle of the load impedance (treatment of such is in RDH) that the tube will see.

    msl

    
    
    

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    • my envelope scratching.... - Jim Doyle 12:19:44 10/15/06 (1)
      In Reply to: Re: that load line will be nearly horizontal.... posted by mqracing on October 15, 2006 at 09:43:04:

      Yeah, I know its ellipsoidal. I'm just illustrating a point that you
      envelope scratch by drawing a loadline thats flat for an interstage...The envelope scratching part that I left out is that if you know Lpri, then you can calculate f-3db very easily too once you know your drivers Rp. However, what the envelope scratching isnt going to tell you is how far out on the HF you can go... With the Lundahl, strapped Alt V, its around 26 kHz due to awhole bunch of
      other transformer parameters that we've neglected. For that, check out the lumped reactance models of transformers in SPICE.

      Unfortunately, I'm a physical chemist and not an EE.... Some
      mathematical training in my past allows me to plunge head first into
      other peoples professions. Fortunately, my plungings thus far are limited to electrical engineering, and not more disastrous choices such as, lets say, civil engineering, or economics. :) :) :) On
      the other hand, I'd never be dumb enough to try to be Secretary of Defense. :)

      -- Jim
      
      

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      • Re: my envelope scratching.... - mqracing 23:11:27 10/16/06 (0)
        In Reply to: my envelope scratching.... posted by Jim Doyle on October 15, 2006 at 12:19:44:

        Hi Jim:

        Nice post and it made me smile. You've done some nice work so don't sweat it!!!!

        yes, I too simplified the analysis... and I was very tempted to write to the original poster and also mention that going to way more complex models that perhaps captures more of the interactions and behaviours of circuits also carries the real risk of "paralysis by analysis"....

        If you want to run for office just let me know... and I'll vote for you twice!!!

        MSL
        
        

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    • Re: that load line will be nearly horizontal.... - Balle Clorin 10:12:39 10/15/06 (1)
      In Reply to: Re: that load line will be nearly horizontal.... posted by mqracing on October 15, 2006 at 09:43:04:

      Well I have got the RDH, but must have missed that reactance part.

      Jims explanation is easy for me to understand, and also fits what I later found in RDH page 519 (chapter 12). I guess the more rigorous calculations must be in some other chapters.?..

      Best regards
      Balle
      

      • RDH link   (Open in New Window)

      
      

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      • Re: that load line will be nearly horizontal.... - mqracing 11:17:11 10/15/06 (0)
        In Reply to: Re: that load line will be nearly horizontal.... posted by Balle Clorin on October 15, 2006 at 10:12:39:

        if you have RDH fourth edition see pages 32 through 34.

        for more info in RDH on elliptical loadlines please see the index.

        msl
        
        

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  • primary's inductance? - keto 09:39:20 10/15/06 (0)
    In Reply to: that load line will be nearly horizontal.... posted by Jim Doyle on October 15, 2006 at 09:26:39:

    Wouldn't the primary's inductance be in parallel with the reflected load? --keto
    
    

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