SET Asylum

" A mu of 100 tube is usually used in a two stage DC 2A3 amp"

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GSH

A

In Reply to: RE: Fi 2A3 mono amps v. this (see photo) posted by drlowmu on February 23, 2015 at 15:49:50

This is not true. It is usually used in an DC 2A3 amp owned by Jeff.

Assuming anybody who runs a 3W amp, already has efficient "enough" speakers,
then the choice is this:

Do you want to attenuate more than 50% of your source signal, accept a certain amount of HF rolloff and unnecessary distortion?

OR

attenuate just 0-15%, have zero HF rolloff and significantly less distortion ?

Some will no doubt "prefer" the former, for metaphysical reasons, OK.
Some will discover the later will be more satisfying for obvious reasons.

Follow Ups:

RE: " A mu of 100 tube is usually used in a two stage DC 2A3 amp" - PakProtector 17:37:26 03/17/15 (0)
Try one of the smaller power pentodes. 6AQ5, 6V6, EL84, or 6CL6 for instance. Run a maximum of 10k plate loads. Enjoy the irony that the driver stage is capable of producing more power than the power tube...:) Match g2 voltage carefully to the load and idle point.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
Thanks for the different perspective, GSH. nt - soulvibrations 10:26:08 02/24/15 (7)
nt
- RE: Thanks for the different perspective, GSH. nt - drlowmu 10:53:29 02/24/15 (6)
  See his last sentence, URL below, two stage DC amp.
  
  GSH just never did his as best as it should be done, with Rk bypassing. Thats OK.
  
  MOST 2 stage DC amps use a mu of 70 or higher ( eg mu 100) tube, ie : 1947 Robin/Lipman, 1960s Asano, 1970s Shishido and 1990's Garber, Uthus, and Fraker.
  
  Jeff Medwin
  - http://www.audioasylum.com/forums/tubediy/messages/23/237843 (Open in New Window)
  - Wrong link. nt - kyle 10:56:48 02/24/15 (5)
    .
    - Its correct - drlowmu 14:19:46 02/24/15 (4)
      Read his last three paragraphs. He too never properly bypassed Rks, but he is talking about doing that now, in the referenced post. Thanks for looking. Regards.
      
      Jeff Medwin
      - The link is to a post by Rage not GSH nt - kyle 14:21:50 02/24/15 (3)
        
        In Reply to: RE: Its correct posted by drlowmu on February 24, 2015 at 14:19:46
        
        .
        
        RE: The link is to a post by Rage not GSH nt - drlowmu 06:30:30 02/25/15 (2)
        
        In Reply to: RE: The link is to a post by Rage not GSH nt posted by kyle on February 24, 2015 at 14:21:50
        
        Sure, thats fine, Rage is discussing his very recent experience - of going back to a mu of 100 12AX7 as a driver in a two stage DC amp, and liking it.
        
        This pertains to what GSH and I were discussing, I see no problem, its on-topic.
        
        Jeff
        
        RE: The link is to a post by Rage not GSH nt - rage 02:56:52 02/28/15 (1)
        
        In Reply to: RE: The link is to a post by Rage not GSH nt posted by drlowmu on February 25, 2015 at 06:30:30
        
        the 12ax7 is better than the 6ej7 pentode (triode strapped) for me right now.
        
        I took some measurements and distortion is slightly lower with 12ax7!
        
        hf rolloff is more but not that much. I will post measurements on the diy forum here pretty soon..
        
        I am actually very surprised by this as I was swayed by the technically correct... and have learned a lot there... but the 12ax7 works IMO. MUCH better than expected.
        
        RE: distortion ... - deathtube 667 03:42:04 03/10/15 (0)
        
        In Reply to: RE: The link is to a post by Rage not GSH nt posted by rage on February 28, 2015 at 01:56:52
        
        You would probably need to run the pentode driver as a pentode w/feedback and measure again to see if the distortion from the driver stage can be lowered.
        
        FWIW, the 7B4/2A3 combo at the standard 60mA operating points produced the best 1W THD% I measured when I had that circuit on a breadboard.

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