K&K Audio / Lundahl Transformers

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K&K Audio / Lundahl Transformers

RE: Using 6sn7 + 6bl7 for SE driver?

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In Reply to: RE: Using 6sn7 + 6bl7 for SE driver? posted by JKT on September 22, 2014 at 14:45:37

Hi JKT, nice work on the Sun amp. I noticed that the 6sn7/6bl7 , each triode half, is used per channel, do you therefor use a CCS per each triode half? I am also inexperienced with the "sound" of using CCS for current sourcing. How would you describe the difference from stock to the of CCS? thank you again for chiming in! best regards, Dak

Follow Ups:

RE: Using 6sn7 + 6bl7 for SE driver? - JKT 16:03:29 09/23/14 (1)
Think of the plate load CCS as replacing the plate load resistor. You would not use the same plate load resistor for each channel. That would result in a mono output like Kevin said, not a stereo output. So yes, each triode half has it's own CCS plate load. I do have to tweak the current output of these in my Sun amp to keep the plate voltages in line so the direct coupling works properly and the driver stage has enough headroom. Such is the problem of living with-in the Sun's limit of 330V B+. Kevin's circuit was designed for the 6SN7/6BN7 and this should NOT be a problem. In my case adding the CCS plate loads is worth the extra hassle that I have to put up with. Less distortion and a more direct connection to the music, is what I hear with the CCSs. While the impedance of a CCS is not infinite, it is very high. As a result the tube can swing quite a bit of voltage with little change in current. As you know, any curve begins to look linear if you look at a small enough section of it. This is true of the plate curves of a triode. Also, the load line with a CCS plate load is practically horizontal. Draw a horizontal line through the plate curves of a triode and you can see that this is a linear load line. Thus the lower distortion and clearer sound. Hope this helps.
- RE: Using 6sn7 + 6bl7 for SE driver? - Tre' 22:21:55 10/06/14 (0)
  "I do have to tweak the current output of these in my Sun amp to keep the plate voltages in line so the direct coupling works properly and the driver stage has enough headroom."
  Am I reading this right.
  Leaving the current the same and just changing the cathode resistor value (thus changing the plate voltage which of course IS the bias voltage for the output tube) can leave you with too little headroom in the driver stage?
  I always liked the idea of an adjustable cathode resistor on the driver tube as the bias adjustment for the output tube with a CCS loaded driver tube and direct coupling.
  And being a SE guy, if I ever build a direct coupled SE amp this is how I would plan to fine tune the bias of the output tube.
  BTW I haven't seen your schematic and I may not understand.
  Tre'
  
  Have Fun and Enjoy the Music
  "Still Working the Problem"
  
  Edits: 10/27/14 10/28/14

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