Tube DIY Asylum

Posted by richardl (A) on May 08, 2007 at 17:45:42

In Reply to: Low vs High Operating Points posted by danlaudionut on May 8, 2007 at 03:45:27:

I think that you want to stay on the load lines, specifically in the flat sections. Extra low or high voltages can get you into the non-linear portions of the curves. Why put up with the distortion?

Current: My experience tells me to never starve my tubes. That doesn't mean I run them all at maxed current but 70-80% of max current is better than low current. Just because you can run it low current does not mean it will still sound good and extend the life of the tubes. You don't want the so-called "perfect sound forever". Low current in the heater and in the B+ should raise distortion and the Radio handbook goes over that. No bargains in good hi-fi. There are those that disagree with me and I have heard a number of amps, preamps etc. that run low current, I think that they are inferior to rich-current equivalents.

• Re: Low vs High Operating Points - danlaudionut 17:52:11 05/08/07 (2)
  In Reply to: Re: Low vs High Operating Points posted by richardl on May 8, 2007 at 17:45:42:

  Richard

  OK 70-80% max rated current.
  What about voltage still 70-80%?
  On the 300B:
  400V/50mA/5K
  VS
  450V/60mA/5K

  DanL
  
  
  
  

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  • Re: Low vs High Operating Points - richardl 14:09:14 05/10/07 (1)
    In Reply to: Re: Low vs High Operating Points posted by danlaudionut on May 8, 2007 at 17:52:11:

    I forgot to ask a question. How much power do you want? The thing about less voltage and less current is you get low Wattage out. I was thinking of drivers where I go for max swing and about 80% of the heater current capacity of the tube. For the 300B, I would go for the linear portion of the curve at 75-80mA, where I think you can do 450V ( which gives 34-36W of dissipation on the plate, which is safe and gets the max power. just looked at the curves, whoa! what a linear tube!) You can always drop down, but design to drive the worst speaker load. Also, if you use the Russian 300B, which is the same as their 2A3 evidently, it is a current pig and low current gives lean bass. However, the tubes will not last as long as they would if you dropped the current and ran them at 450V and 60mA(which makes sense for the expensive 300B's).

    
    http://datasheets.electron-tube.net/sheets/163/3/300B.pdf

    Personally, I am always running out of power... and gain...
    
    

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    • Re: Low vs High Operating Points - danlaudionut 17:42:30 05/11/07 (0)
      In Reply to: Re: Low vs High Operating Points posted by richardl on May 10, 2007 at 14:09:14:

      I am running 93dB speakers and I don't play loud.
      I would still like at least 8 watts though.
      I like to pick the loadline OP point that
      splits the zero bias and zero current point
      so that when it goes to crap it really does.
      It also gives maximum output before distortion.
      400V would give me 10W and 450V would net 8W.
      I haven't decided on which 300B to use.
      I am leaning toward the VA 300B titanium.

      DanL
      
      
      
      

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