• RE: It may not be the tube - rlyach@yahoo.com 06:40:57 07/24/13 (4)
  In Reply to: RE: It may not be the tube posted by Frihed89 on July 24, 2013 at 01:35:27

  Thanks for posting a reply. My conclusion were drawn from both measurements and consulting several people on different forums, and also speaking to a very experienced audiophile who has built many amps. Even the people at Sophia Electric recommended I switch to the Carbon Princess, which I did. The problem is not the lower current operating point in itself, it is trying to get an optimum operating point at a lower current using Kit-1. There are many factors that determine where the tube can and should be operated, including the B+ voltage and the output transformer load. Not just the cathode resistor. The AN Kit-1 is a self biased circuit and B+ is fixed at close to 450V with a 5U4GB rectifier. The output transformer has a DC resistance of about 130 ohms and a musical impedance of 2.7K ohms. Given these limitations just changing the cathode resistors does indeed increase the distortion at full power. If I could change the output transformers, or the B+ than that would be a different story. A higher output transformer impedance and lower B+ will indeed work very well at lower currents with lower distortion. If you have an suggestions on how to achieve a lower current without having to make major (expensive) modifications to my kit-1 I would be very appreciative. Thanks again for your guidance.
  
  

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  • OK - Frihed89 22:19:27 07/24/13 (1)
    In Reply to: RE: It may not be the tube posted by rlyach@yahoo.com on July 24, 2013 at 06:40:57

    Sorry, didn't know what else you knew. I wish i could answer your question since you pinpointed the two things I was thinking about. I am not that familiar with the kit. A suggestion: post a schematic on the DIY forum and ask the same question.
    Observe, before you think. Think before you open your yap. Act on the basis of experience.
    
    
    

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    • RE: OK - rlyach@yahoo.com 06:31:26 07/25/13 (0)
      In Reply to: RE: OK posted by Frihed89 on July 24, 2013 at 22:19:27

      I believe I will just keep my system running where the original designers intended it to be run. There is a reason why this kit has been around for so long :-) There is an easy modification that I could try if I wanted to lower the operating current. Simply put a series resistor in front of the choke to drop B+ to a lower level. I don't believe this will be compatible with the output transformers however. If I decide to build another amp I may try using custom parts and target 70mA or so. As for my kit one, I will enjoy it as it is using solid plates. I really would like to hear a pair of KR 300Bs in this system. The KR tubes are rated at 50 Watts and 120mA, so they should work very well. Thanks for all the help and comments.
      

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  • RE: It may not be the tube - astrostar59 07:15:55 07/24/13 (1)
    In Reply to: RE: It may not be the tube posted by rlyach@yahoo.com on July 24, 2013 at 06:40:57

    Hi
    I am confused by this thread. The Kit1 has been sold for years, with many happy customers. Are we now saying that it is a tube eater? Or is the issue with the Sophia 300b tube?
    
    I would have thought the circuit design of the Kit1 is correctly figured for optimum standard fair 300b tubes to run within tolerance.
    
    I am wondering if your particular Kit1 build has an issue? It might be worth doing some voltage an current checks and pinging Brian for advice on that. Also bear n my (in my experience) that tolerances can go out of wack if feeding speakers with wild impedance swings or none tube friendly 3 way designs.
    
    And I presume you have the amp in a cool environment with no shelf above to reduce air flow. Tubes amps don't like getting too hot or beyond there normal operating ambiant temp of 30°C max.
    

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    • RE: It may not be the tube - rlyach@yahoo.com 07:47:15 07/24/13 (0)
      In Reply to: RE: It may not be the tube posted by astrostar59 on July 24, 2013 at 07:15:55

      The kit one is great! The problem is that the mesh plate tubes can't handle the same dissipation level as solid plates. I bought the mesh plates because they had a good reputation and they looked cool, but I have since discovered that they must be run at a lower bias power. The bias points of kit one are indeed optimum and I have very happy with my kit-1. The folks at Sophia upgraded me to Carbon Princesses and they sound excellent. The bias point of Kit-1 is:
      
      B+ ~450 w/ 5U4GB
      B+ ~430 w/ 5U4G
      V-plate ~360 w/ 5U4GB
      V-plate ~340 w/ 5U4G
      I-plate ~85mA w/ 5U4GB
      I-plate ~82mA w/ 5U4G
      V-cathode ~77V w/ 5U4GB
      V-cathode ~73V w/ 5U4G
      
      All these measurements were made with Sophia Carbon Princesses. JJ 300B's gave a slightly lower I-plate. If you calculate the power dissipation at these levels you get:
      
      W-Plate ~31 Watts w/ 5U4Gb
      W-Plate ~28 Watts w/ 5U4G
      
      Notice that I included numbers for both 5U4G and 5U4GB. The 5U4G is a better choice in my opinion but the GB version is usually included in the kit, so I included these numbers for reference.
      
      From what I have read, the mesh plates can't handle this continuous power. All the solid plates can, and I have had no problems with Shuguang, Psvane, JJ, and Sophia Carbon Princesses. I am currently running the Carbon Princesses. They seem to open up the sound a little more.
      
      kit-1 is indeed a great circuit and I am very happy with it. I only ran into trouble with Sophia Mesh Plates.
      
      here are a few pics of my build. Notice that the mesh plates are indeed running a little hot:
      
      https://dl.dropboxusercontent.com/u/109856281/17-Finished%20A0.jpg
      https://dl.dropboxusercontent.com/u/109856281/17-Finished%20A2.JPG
      https://dl.dropboxusercontent.com/u/109856281/AN-K1-2.jpg
      https://dl.dropboxusercontent.com/u/109856281/IMG_0255.JPG
      
      

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