SET Asylum

• RE: Link to Thorsten's Legacy 300B - Mr_Steady 10:16:35 11/23/14 (0)
  In Reply to: RE: Link to Thorsten's Legacy 300B posted by Jim Dowdy on November 23, 2014 at 06:24:09

  
  
  

  
  "I have no experience with this circuit - provided for informational purposes."

  Yes that's it. I didn't remember it with an SV83/6P15P.

  Does anybody have any experience with this type of tube regulated power supply? If somebody wanted to explain how this differs from using a gas voltage regulator tube, then I would greatly appreciate it. Are both useful in lowering hum?

  Thanks in advance for any replys,

  Jamie
  
  Big speakers and little amps blew my mind!
  
  

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  Edits: 11/23/14
• That's Dowdy Lama! Yep, that's one of the first versions.... - Ivan303 07:34:46 11/23/14 (3)
  In Reply to: RE: Link to Thorsten's Legacy 300B posted by Jim Dowdy on November 23, 2014 at 06:24:09

  But I seem to recall he made some additional changes in order to flatten the frequency response in the version that DIY HIFI Supply eventually sold as a kit. I think he discusses it in the post below which no longer contains links to the schematics.
  
  "A last trick is implemented in a pair of 1nF capacitors between the 300B Anode and 310A screengrid. This is actually positive feedback at high frequencies. This helps to overcome the HF rolloff inherent to the classic 91 Circuit, where usually 20KHz is around 3db down. In my Amp's I measure -3db somewhere at around 75KHz with this positive feedback in place, without -3db is around 20KHz as expected."
  
  Also the 'optimized WE Cathode Bypass' which he discusses and which I suspect was likely the precursor to Jack Eliano's 'Ultrapath' circuit and which I have already implemented in my 300B amps.
  
  I think, all and all, with his circuit description below and the circuit diagrams in page you linked to, one could pretty much duplicate the final product I heard at RMAF so many years ago.
  
  Link below:
  
  
  
  

  • Thorsten's   (Open in New Window)

  
  

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  • Schema. - RC Daniel 12:03:32 11/23/14 (1)
    In Reply to: RE: That's Dowdy Lama! Yep, that's one of the first versions.... posted by Ivan303 on November 23, 2014 at 07:34:46

    Hey Ivan, I did not notice that the schema had been removed from that post.

    Here it is:

    
    
    

    Note, this design uses the partial WE connection: 50uF cathode bypass capacitor with 15uF B+ to cathode capacitor. Thorsten's later (DRD) amps used the full B+ to cathode connection (50uF+ using multiple capacitors in parallel) with no cathode bypass capacitor.

    Cheers.
    
    "In the beginner's mind there are many possibilities, in the expert's mind there are few." Shunryo Suzuki
    
    

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    Edits: 11/23/14

    • Yes, that's it.... - Ivan303 14:57:10 11/23/14 (0)
      In Reply to: RE: Schema. posted by RC Daniel on November 23, 2014 at 12:03:32

      That's just about the same circuit that ended up in the DYI HIFI Supply WE91 SET amp.
      
      Sure would like to take a whack at upgrading my current 300B amps but would be a LOT of work. Might try it with an octal driver with a 6V heater of some sort, like the 6J7.
      
      
      
      
      
      
      

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  • Make that "Thanks, Dowdy Lama"... - Ivan303 07:55:50 11/23/14 (0)
    In Reply to: RE: That's Dowdy Lama! Yep, that's one of the first versions.... posted by Ivan303 on November 23, 2014 at 07:34:46

    Should never post before the second cup of coffee!
    
    
    
    
    

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