Tube DIY Asylum

Posted by kellymon (A) on November 06, 2009 at 19:09:07

I'm finishing another amp build and I am seriously considering trying battery bias on the driver again.
Previously, when I tried it in another amp, it sounded ok, but I gave a "slight" edge to R/C cathode bias on a cap coupled 2 stage amp.
And I'm a little concerned about battery life, what happens when it fades and how do you know?
I've read most of the archives here and elsewhere.... it seemed like there was a flurry a few years ago, but not much discussion lately....

So I'm wondering, if you've tried it, are you still using it...why or why not?
robert

Edits: 11/06/09

• Suitable grid resistor for battery bias? - andy evans 02:58:39 11/08/09 (1)
  In Reply to: RE: Battery Bias; Are you using it? Why or Why not? posted by kellymon on November 06, 2009 at 19:09:07

  Hi - never tried this - what's a suitable grid resistor to use with battery bias for a preamp with a 26 tube?
  

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  • RE: Suitable grid resistor for battery bias? - Poindexter 09:26:51 11/08/09 (0)
    In Reply to: RE: Suitable grid resistor for battery bias? posted by andy evans on November 08, 2009 at 02:58:39

    Andy, battery bias is 'fixed' bias.  Look at the device's rating for Rg-k under this service.  For directly heated valves, this rating is typically low (in ohms).  Evidently, they will draw some grid current.
    
    Aloha,
    
    Poinz
    AudioTropic
    

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• RE: Battery Bias; OT - FenderLover 10:34:58 11/07/09 (4)
  In Reply to: RE: Battery Bias; Are you using it? Why or Why not? posted by kellymon on November 06, 2009 at 19:09:07

  Do batteries add any tonal signature to a system? Versus a conventional power supply.
  
  
  Thanks!
  

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  • Definitely - danlaudionut 12:02:21 11/07/09 (3)
    In Reply to: RE: Battery Bias; OT posted by FenderLover on November 07, 2009 at 10:34:58

    

    FL
    
    The pink trace is the noise spectra of an unloaded battery.
    The blue trace is the noise spectra of discrete low noise regulator.
    The cyan trace is the battery with a load of 35mA.
    Batteries do have noise under dynamic load.
    
    Also read here and link below for more -
    http://diyparadise.com/web/index.php?option=com_content&task=view&id=96&Itemid=5
    
    DanL
    
    
    
    

    • http://diyparadise.com/web/index.php?option=com_content&task   (Open in New Window)

    
    

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    • much thanks - FenderLover 23:08:39 11/07/09 (1)
      In Reply to: RE: Definitely posted by danlaudionut on November 07, 2009 at 12:02:21

      Is there a sonic signature? One that a person could tell simply from listening to a unit with battery power?
      

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      • RE: much thanks - danlaudionut 23:53:53 11/07/09 (0)
        In Reply to: RE: much thanks posted by FenderLover on November 07, 2009 at 23:08:39

        FL
        
        Usually it is the lower noise floor
        creating a blacker back drop for the music
        which is less noise between the notes.
        Some call it downward dynamic expansion.
        
        DanL
        
        
        
        
        

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    • The graph looks suspicious... - Lee of Omaha 14:34:32 11/07/09 (0)
      In Reply to: RE: Definitely posted by danlaudionut on November 07, 2009 at 12:02:21

      The peaks correlate very well from source to source. There is no reason that I can think of that batteries and and other source should generate essentially the same noise spectra. It seems more likely that the battery is a better filter of extraneous noise. The 50 Hz peak is especially suspicious--were these spectra taken in Europe?
      
      Lee
      

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• RE: Battery Bias Reliability - Neff 05:56:17 11/07/09 (1)
  In Reply to: RE: Battery Bias; Are you using it? Why or Why not? posted by kellymon on November 06, 2009 at 19:09:07

  Place a dedicated volt meter on the chassis to monitor battery voltage or have test points with easy access using a remote meter.
  

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  • External test points... great idea! - kellymon 14:53:10 11/07/09 (0)
    In Reply to: RE: Battery Bias Reliability posted by Neff on November 07, 2009 at 05:56:17

    Neff,
    Thanks for that suggestion, I like the idea of a volt meter, but probably not on this amp.....but externally accesable test points for the battery bias is a fine idea.
    
    I should have thought of that myself, main amp is a Dynaco ST70 and it gets checked every month or 2 via the external test points...
    robert
    

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• RE: Battery Bias; Are you using it? Why or Why not? - JANDG 05:09:11 11/07/09 (1)
  In Reply to: RE: Battery Bias; Are you using it? Why or Why not? posted by kellymon on November 06, 2009 at 19:09:07

  In the cathode position I have not had a NiMH read bad yet & even after 2-3 years.I allways after listening on kitchen table when building choose the NiMH for drivers it seems over R/C on cathode. Also had good luck with useing Dewalt power tool batteries ran in series if needed on cathode of outputs & even on g1 fixed bias. I like the sonics better eathier way useing batteries.
  Joe
  Wisdom for today.........
  A GREAT tube amp or speakers will allways be GREAT & bieng relevant today is irrelevant.
  
  

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  • Cool, thanks! (nt) - kellymon 14:55:30 11/07/09 (0)
    In Reply to: RE: Battery Bias; Are you using it? Why or Why not? posted by JANDG on November 07, 2009 at 05:09:11

    nt
    

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• RE: Battery Bias; Are you using it? Why or Why not? - gluca 21:18:10 11/06/09 (7)
  In Reply to: RE: Battery Bias; Are you using it? Why or Why not? posted by kellymon on November 06, 2009 at 19:09:07

  Do you mean you want to bias the tube at the grid (1) or with a battery at the cathode (2)?
  
  (1) it would last many many months ... I check them every 6 months and they are OK. The voltage fades away slowly so you are on the safe side
  
  (2) get a rechargeable (capacity = 10x the bias current) and you are fine "for ever"
  

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  • RE: Battery Bias; Are you using it? Why or Why not? - twystd 21:32:27 11/06/09 (1)
    In Reply to: RE: Battery Bias; Are you using it? Why or Why not? posted by gluca on November 06, 2009 at 21:18:10

    I run a NiMh, on the cathodes of my 6SL7 driver, really like it, I change the batteries out about once a year to be on the safe side.
    
    twystd
    

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    • RE: Battery Bias; Are you using it? Why or Why not? - kellymon 14:57:23 11/07/09 (0)
      In Reply to: RE: Battery Bias; Are you using it? Why or Why not? posted by twystd on November 06, 2009 at 21:32:27

      Thanks for that, I saw in past posts that you had used it, but I wasn't sure how well it stood the test of time with you.
      Good to know you still like it:)
      robert
      

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  • RE: Battery Bias; Are you using it? Why or Why not? - kellymon 21:30:57 11/06/09 (4)
    In Reply to: RE: Battery Bias; Are you using it? Why or Why not? posted by gluca on November 06, 2009 at 21:18:10

    Hi,
    That would be replacing the cathode resistor/cap with a battery, in my case a NiMH @ about 1.2-1.3v.
    Yes, the general rule with batteries in most applications seems to be at least 10X battery capacity vs current.
    No problem there, my Duracell pre-charged (slow self discharge) NiMH says 2000 mAh and I'm only drawing 7.3 ma.
    
    Can I assume from your reply that you use this form of bias and like it?
    thanks,
    robert
    

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    • no - gluca 13:14:59 11/07/09 (3)
      In Reply to: RE: Battery Bias; Are you using it? Why or Why not? posted by kellymon on November 06, 2009 at 21:30:57

      I always have the cathode at ground and bias the grid negative by the batteries (via the secondary coils of the input transformer). I do prefer going this way.
      
      gianluca
      

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      • Agree - Naz 04:24:02 11/08/09 (2)
        In Reply to: RE: no posted by gluca on November 07, 2009 at 13:14:59

        Grid bias using lithiums makes the most sense to me. Virtually no current provides for an extremely stable and virtually noise free bias source and is out of the direct signal path where the most damage is done.
        
        Naz
        

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        • Eager to try that - pix 12:10:15 11/08/09 (1)
          In Reply to: RE: Agree posted by Naz on November 08, 2009 at 04:24:02

          Hi Naz
          I have´nt tryed that yet, byt eager to try.
          Do you remove the output shunt resisistor (often 1M) om the previous stage to save battery capacity, or do you add a input cap?
          
          Does it really make any difference if the Li-battery is serial connected to the grid leak resistor, or right on the grid
          The signal circuit is the same?
          
          Regards
          Pix
          Sweden
          
          

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          • RE: Eager to try that - Naz 14:59:32 11/08/09 (0)
            In Reply to: RE: Eager to try that posted by pix on November 08, 2009 at 12:10:15

            Hi Pix,
            
            If you're not using an IT like Gluca, then this typical circuit shows a couple of examples of wiring so there is no DC idle current from the battery.
            

            
            
            

            
            Rgds,
            Naz
            

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