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  • Grid leak resistor question

    Hello. What are the pros and cons using one shared grid leak resistor vs individual grid resistor on each tube on each semialternance when using multiple pairs please ? Eg.Why to use 22nF/220k on each power grid and not shared 47nF/100k for each pair, for instance ? There is a reason to not share the same input when using pairs which do the same job,please?
    Last edited by catalin gramada; 08-08-2020, 10:22 PM.
    "If it measures good and sounds bad, it is bad. If it measures bad and sounds good, you are measuring the wrong things."

  • #2
    One thing I'm considering is that if there's a bad tube or a failure with voltage leaking onto or even shorted to a grid then that voltage would be elevated on the shared grid leak resistor and threaten the other tube on that side.
    "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

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    • #3
      Originally posted by catalin gramada View Post
      Hello. What are the pros and cons using one shared grid leak resistor vs individual grid resistor on each tube on each semialternance when using multiple pairs please ? Eg.Why to use 22nF/220k on each power grid and not shared 47nF/100k for each pair, for instance ? There is a reason to not share the same input when using pairs which do the same job,please?
      Not quite sure what you mean (what is semialternance?). Drawings would help.

      I think you are speaking of PP stages with more than 2 tubes. The coupling cap must sit before the grid leak resistor as the grid needs a DC path to ground (actually to the cathode), so with only one coupling cap individual grid leaks would be in parallel anyway. So typically each side shares one coupling cap and one grid leak resistor, while grid stoppers should always be individual.
      A reason to use individual coupling caps and grid leaks per tube would be if you need to be able to bias each tube individually..
      Last edited by Helmholtz; 08-08-2020, 11:00 PM.
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      • #4
        By "semialternance" I think Catlin is referring to the half cycle 'push' vs 'pull' side. Although it's not a word maybe it should be! It's quite descriptive.
        Experience is something you get, just after you really needed it.

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        • #5
          Originally posted by nickb View Post
          By "semialternance" I think Catlin is referring to the half cycle 'push' vs 'pull' side. Although it's not a word maybe it should be! It's quite descriptive.
          Yes, from the context and applying my Latin recollection I figured it might mean half-cycle (maybe Spanish?) but I like to make sure.
          Last edited by Helmholtz; 08-09-2020, 09:44 PM.
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