Posted by thermionic addictions (A) on June 19, 2006 at 14:39:26

Is there a simple formula for determining the inductance/current,
when using a choke plate load? I know how to determine a plate
resistor using the tubes curves. But a choke seems to me to
throw a curve (pun not intended) ball at the whole thing.
Maybe I am just over thinking this. But if anyone can give me some pointers I would appreiciate it. Thanks.
Cal

• Re: choke loaded plates - KevinC 19:26:55 06/19/06 (4)
  In Reply to: choke loaded plates posted by thermionic addictions on June 19, 2006 at 14:39:26:

  The big deal here is to make sure that the choke has enough inductance to provide adequate low frequency response in interaction with the tube chosen. The easy way to calculate the approximate low frequency limit here defined as the -1dB point is to use the following equation:

  Frequency (-1db) = parallel combination of the anode resistance of the tube and the load resistance divided by the quantity, anode choke inductance times 3.14 (pi)

  You can ignore the load resistance, if it is more than 10 times the anode resistance of the tube.
  
  Kevin Carter
  K&K Audio
  www.kandkaudio.com
  
  

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  • OK after playing with the math a little bit.... - thermionic addictions 11:24:40 06/20/06 (2)
    In Reply to: Re: choke loaded plates posted by KevinC on June 19, 2006 at 19:26:55:

    it would appear to me that essentially, you can't have too much
    inductance.
    What effect does the DCR of the choke (other than the
    obvious voltage drop) have on this kind of circuit.
    If a lower henry, lower DCR choke, would keep the circuit in a reasonable
    frequency range would this be better than a higher henry, higher DCR
    choke? Or would it make any difference.
    Cal
    
    

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    • Re: OK after playing with the math a little bit.... - KevinC 14:37:57 06/20/06 (1)
      In Reply to: OK after playing with the math a little bit.... posted by thermionic addictions on June 20, 2006 at 11:24:40:

      As with most things, to get a little of this you have to give up a little of that. If you keep increasing the inductance, either through more turns of wire or through using a larger core, you will inevitably increase the amount of stray capacitance and start seeing aberations in the high frequency response. I typically am very satisfied with a single stage low frequency cut-off (-1dB) of 5-10Hz. Incorporating that into a multi-stage amplifier might change my opinion, though, due to the desire to stagger roll-offs a bit.

      Of course there are probably others who think differently, but I don't give too much weight to DCR with plate chokes. Obviously, the choke has to be designed to carry the DC current without too much heating. That is usualy enough to preclude too much DCR.
      
      Kevin Carter
      K&K Audio
      www.kandkaudio.com
      
      

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      • Very cool kevin. Thanks for the excellent answers. (nt) - thermionic addictions 14:55:20 06/20/06 (0)
        In Reply to: Re: OK after playing with the math a little bit.... posted by KevinC on June 20, 2006 at 14:37:57:

        nt
        
        

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  • Thanks Kevin. That is exactly what I wanted to know. - thermionic addictions 08:50:26 06/20/06 (0)
    In Reply to: Re: choke loaded plates posted by KevinC on June 19, 2006 at 19:26:55:

    nt
    
    

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