Posted by Uncle Clyde (A) on June 12, 2008 at 06:46:25

Mikey,

I like the design that you and Kevin came up with! How could this design be adapted to parallel output tubes(Kt77) ? (open can of worms now). Could I just add another pair of tubes and current sources or will I need different grid chokes and drivers?

Thanks,
Clyde

• http://www.audioasylum.com/forums/magnequest/messages/7472.html   (Open in New Window)

• RE: Re: EL-34 schematic ( special "can of worm" edition) - mqracing 09:41:45 06/13/08 (0)
  In Reply to: RE: Re: EL-34 schematic ( special "can of worm" edition) posted by Uncle Clyde on June 12, 2008 at 06:46:25

  Hi Clyde:
  
  With the changes that Kevin and you have discussed I think you will be fine.
  The grid chokes (BCP-16 GC) will work equally as well in your proposed circuit modification.
  
  However, I would encourage you to look at part 2 of Kevin's post right above this thread---- and check out the IT coupled circuit which could easily be modified with your ideas\goals in mind.
  
  
  MSL
  
  
  
  Builder of MagneQuest™ & Peerless™ transformers since 1989
  
  
  

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• RE: Re: EL-34 schematic ( special "can of worm" edition) - KevinC 07:46:15 06/12/08 (2)
  In Reply to: RE: Re: EL-34 schematic ( special "can of worm" edition) posted by Uncle Clyde on June 12, 2008 at 06:46:25

  Yes, you could use a push-pull parallel pair of KT77s per channel without any changes to the driver or the chokes. It would be advisable, if you want the greater power made possible by 4 output tubes, to use a lower plate impedance output transformer to reflect the lower total plate impedance of the output stage. Of course as you note, you will need to add a current source for each additional tube to keep the thermal load on the current sources moderate.
  
  Kevin Carter
  K&K Audio
  www.kandkaudio.com
  
  

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  • RE: Re: EL-34 schematic ( special "can of worms" edition) - Uncle Clyde 08:49:32 06/12/08 (1)
    In Reply to: RE: Re: EL-34 schematic ( special "can of worm" edition) posted by KevinC on June 12, 2008 at 07:46:15

    Thanks Kevin,
    
    My output transformer is 2.3K. I will be using your cascoded ccs.
    
    Would a pot between the cathodes of each output tube pair be of use to keep good balance, or will the ccs do that?
    
    Clyde
    
    
    
    

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    • RE: Re: EL-34 schematic ( special "can of worms" edition) - KevinC 09:52:21 06/12/08 (0)
      In Reply to: RE: Re: EL-34 schematic ( special "can of worms" edition) posted by Uncle Clyde on June 12, 2008 at 08:49:32

      Tube matching was addressed as part of the discussion of the original circuit, but in short, you should use reasonably matched tubes and then not worry about the residual imbalance. The CCS make for good AC balance and DC balance isn't worth worrying about until you start to see big imbalances (> 15% of bias current). I suspect that this is not a universally acceptable view, but the loss of a few Hz of bass response is nothing that I would lose sleep over.
      
      Kevin Carter
      K&K Audio
      www.kandkaudio.com
      
      

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