Posted by nullspace (A) on October 26, 2009 at 15:41:12

In Reply to: RE: Follow-Up posted by nullspace on October 26, 2009 at 10:03:14

Just add some details, measuring the DC voltage across the four EXO-003 plate-loading chokes w/ the parafeed DC-blocking caps in place, one channel measured .35mA DC-unbalance and the other .46mA. So, I'm pretty comfortable taking out caps and running the amps without them in place. Better to be lucky than good, I suppose.

EDIT: I'm guessing that the way to calculate the DC-unbalance is the difference in DC current draw of the two 2A3s. Should I instead, w/ the DC-blocking caps removed, measure the DC voltage from end-to-end of the S240A primary, then w/ DCR of the winding calculate DC-unbalance that way? A little help here would be appreciated.

Regards,
John

Edits: 10/26/09   10/26/09   10/26/09

• RE: Follow-Up - Colonel Sanders 05:36:18 10/31/09 (4)
  In Reply to: RE: Follow-Up posted by nullspace on October 26, 2009 at 15:41:12

  I personally think that the ''complexity'' required to avoid DC unbalance defeats the purpose and kills the kill the beauty of the SA240.
  
  I have lived with my perfectly unperfect Seth for quite a while now. I think I found happiness. I designed the Seth in 2004 after that, the obsession that started as hobby came to a halt.
  Sounds like chicken!
  
  

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  • RE: Follow-Up - mqracing 13:39:40 11/02/09 (3)
    In Reply to: RE: Follow-Up posted by Colonel Sanders on October 31, 2009 at 05:36:18

    if it smells like... err... sounds like chicken... then the Colonel must have built it!!!
    
    Still "down under"... got any silver to send me yet???
    
    my initial attraction to the idea of parafeed PP was largely the product of wondering what effect if any having separate paths for the AC and DC paths would have... and if the resultant "improvement" in PSRR would make a difference...
    
    like I said in an earlier post... I might have gone with SUPER plate chokes (i.e., much higher L's)... though this is not meant to fault the good work of nullspace...
    
    and my other thought... that I was going to mention in a response to one of nullspace's posts... I'll say it here...
    
    I think nullspace has only tried one brand (and one value?) of blocking cap... I would assemble a handful of candidates of varying constructions and give try out different brands, values, and cap materials.
    
    Motor runs, Jensen oil\copper caps (available through K&K audio), old (i.e., vintage) oilers, etc.
    
    Caps do have voices... but so don't transformers... and tubes... and perhaps even the choice of solder... so I don't interpret this as a "fault" or shortcoming of capacitors (no capcitoritis here)...
    
    but it is worth exploring the variations... just as various brands and materials of resistors can make subjective differences in sound....
    
    ya gotta try a few to hone in on the guys who are going to work best for your application and your ears.
    
    
    cheers all,
    
    Mike
    
    
    
    
    
    Builder of MagneQuest™ & Peerless™ transformers since 1989
    
    
    

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    • RE: Follow-Up - Colonel Sanders 06:49:13 11/05/09 (0)
      In Reply to: RE: Follow-Up posted by mqracing on November 02, 2009 at 13:39:40

      Yep, still down under.
      
      And I'll be here for a while as I just got my permanent residency.
      
      The weather is fantastic around here.
      Sounds like chicken!
      
      

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    • RE: Follow-Up - nullspace 14:48:36 11/02/09 (1)
      In Reply to: RE: Follow-Up posted by mqracing on November 02, 2009 at 13:39:40

      Hi Mike,
      
      I meant to post a follow-up vis-a-vis the caps... Currently, I'm listening to the amp set up PP parafeed with the DC-blocking caps in circuit, but with the primary's center-tap lifted off of ground, and am hearing none of 'the edginess, maybe almost stridency with voices' I mentioned earlier. So, more a consequence of the circuit and less the capacitor's fault, I suppose.
      
      You've said a couple times that you would've recommended more H in the plate chokes; could you speak a bit more about this? I would've thought that if the EXO-003 is good enough for a 2A3 SE circuit, it would at least be in the ballpark for a PP application. I get the feeling that you think the EXO-003 isn't nearly enough here...
      
      Regards,
      John
      

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      • RE: Follow-Up - mqracing 18:44:31 11/02/09 (0)
        In Reply to: RE: Follow-Up posted by nullspace on November 02, 2009 at 14:48:36

        Hi John:
        
        My sense of perhaps wanting to see a larger L plate choke has to do with that as the impedance of the plate choke becomes larger and larger it will have less and less effect on the effective impedance of the output transformer.
        
        The L of the plate choke is going to be in most cases the limiting factor and even with our larger plate chokes it will most likely be the smallest of the paralleled impedances... hence it "limits" the net impedance that the anode of the tube will see.
        
        But with more thought I am not now so sure that I would strictly urge you to abandon your 003's and go with something larger... the 003's themselves as you rightly point out should have enough L to adequately load a 2A3.
        
        So allow me to modify my advice... and carry on forward with your present game plan.
        
        
        Mike
        
        
        
        Builder of MagneQuest™ & Peerless™ transformers since 1989
        
        
        

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• RE: Follow-Up - danlaudionut 09:32:41 10/27/09 (1)
  In Reply to: RE: Follow-Up posted by nullspace on October 26, 2009 at 15:41:12

  John
  
  Since you want to know the current draw
  across the S240A primary then the method
  you said about measuring the DC across
  the primary would be the way to go.
  
  DanL
  
  
  
  
  

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  • RE: Follow-Up - nullspace 09:55:46 10/27/09 (0)
    In Reply to: RE: Follow-Up posted by danlaudionut on October 27, 2009 at 09:32:41

    Thanks Dan. The more I thought about it last night, the more it seemed obvious that is the relevant measurement.
    
    Regards,
    John
    

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