• RE: URGENT LUX91 Mono FCUPS power supply schematics - siepi 11:04:51 06/18/13 (2)
  In Reply to: RE: URGENT LUX91 Mono FCUPS power supply schematics posted by Thorsten on May 05, 2013 at 00:14:17

  Hi Thorsten
  
  i just got a message from my repair guy saying that he is giving up .
  he is not able to fix the amp which keeps blowing the mosfet in the power supply no matter what he tries.
  there seems to be no detailed documentation about the accurate values of the components on the power supply because it went through different stages .and without that information it is not ossible to fix it .
  
  as of now i am left w/ a very heavy paperweight .
  
  can you or simon offer to repair the amp ?
  at this time this seems to be the only option to get it playing again .
  i thought i could avoid shipping to HK but if that is what it takes to resolve this issue i will do it .
  
  please advise how best to proceed .
  
  thanks
  

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  • RE: URGENT LUX91 Mono FCUPS power supply schematics - Thorsten 11:27:10 06/18/13 (1)
    In Reply to: RE: URGENT LUX91 Mono FCUPS power supply schematics posted by siepi on June 18, 2013 at 11:04:51

    Hi,
    
    If the Amp blows the Mosfet there is a short or excessive current somewhere.
    
    Which Mosfets goes, the one for the negative bias (alone on it's heatsink) or for the HT (two next to each other)?
    
    Normally one should power up the amplifier without output tube, check that voltages are sensible (around 450V HT, Bias starting at around -120V and slowly falling.
    
    The circuits are not complex or unusual, any competent service tech should be able to handle this.
    
    Ciao T
    
    Sometimes I'd like to be the water
    sometimes shallow, sometimes wild.
    Born high in the mountains,
    even the seas would be mine.
    
    (Translated from the song "Aus der ferne" by City)
    
    

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    • RE: URGENT LUX91 Mono FCUPS power supply schematics - siepi_70@hotmail.com 11:39:15 06/19/13 (0)
      In Reply to: RE: URGENT LUX91 Mono FCUPS power supply schematics posted by Thorsten on June 18, 2013 at 11:27:10

      Hi Thorsten
      
      i sent you a PM through Audioasylum .
      
      
      

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• Hello 'T', off topic... - Ivan303 08:19:51 05/27/13 (1)
  In Reply to: RE: URGENT LUX91 Mono FCUPS power supply schematics posted by Thorsten on May 05, 2013 at 00:14:17

  THe WE 'reissue' 300B's in my more or less stock DIY HiFi Billies are getting a bit long in the tooth.
  
  Any suggestions for replacements?
  
  Using NOS Tung Sol 6SU7 in the driver section with battery bias and grid chokes.
  
  Thanks.
  
  
  

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  • RE: Hello 'T', off topic... - Thorsten 10:57:10 06/05/13 (0)
    In Reply to: RE: Hello 'T', off topic... posted by Ivan303 on May 27, 2013 at 08:19:51

    Hi,
    
    My "favourite" 300B is as follows:
    
    TJ 300B Mesh Plate
    350V/60mA Operating point (means around 1.2K cathode R for self bias)
    5-6K Load impedance (mismatch the transformer - treat 4R output as 8R)
    
    This overall reduces output power (you get around 7 Watt) and moves the sound into the direction of the 45.
    
    Add a D3a as driver stage (Resistor Load 22K is ok, CCS or Choke more better; bias - choose your poison aim for 170V/10mA appx.)
    
    Sadly consistency at TJ has been slipping, so only buy them local, tested and selected by the seller and with a decent warranty.
    
    If you want traditional WE Style Sound keep the 350V/80mA/2.5...3K and get either WE Replicas or Svetlana's. Sadly my experiences with the Svetlana's in terms of longevity has not been great, so see above for sourcing.
    
    There are a lot new "brands" and "models" of 300B out there, which to me look all like Shugang/Guagang/Sovtek/Svetlana fayre on the inside (or rebranded TJ), gussied up and sold at obscene markups. So I never tried them...
    
    I did like the Vaic/EML tubes I tried, however there are issues with supply/consistency/warranty, so only buy local with solid warranty.
    
    As an aside, if you can live with low power, I quite like the recently introduced Shugang/Guagang 2A3B (single Anode) which is one of the few 2A3 I actually like. Sticking them into a Billie suitably modified (I like the old DC coupled JC Morrison design from the Fi Primer with 6SL7 SRPP driver) makes a very nice and inexpensive Amp.
    
    Ciao T
    
    Sometimes I'd like to be the water
    sometimes shallow, sometimes wild.
    Born high in the mountains,
    even the seas would be mine.
    
    (Translated from the song "Aus der ferne" by City)
    
    

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• RE: URGENT LUX91 Mono FCUPS power supply schematics - siepi 10:42:57 05/14/13 (0)
  In Reply to: RE: URGENT LUX91 Mono FCUPS power supply schematics posted by Thorsten on May 05, 2013 at 00:14:17

  Hi Thorsten
  
  i will ask my repair technician about details and will post .
  i just received the schematics from Simon and hopefully that will help .
  
  thanks
  

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