Posted by GTCharlie (A) on January 16, 2008 at 01:28:55

In Reply to: RE: 5687 instead of 6sh7 in interstage amplifiers? posted by richardcooper2k on January 15, 2008 at 15:47:53

you can parallel a 5687 for around 70mA driving current. plus you get a better impedance match.

but check 5687 tube curves to determine your operating points. You may have to have a separate mains transformer.

• RE: 5687 instead of 6sh7 in interstage amplifiers? - GTCharlie 19:39:45 01/16/08 (2)
  In Reply to: RE: 5687 instead of 6sh7 in interstage amplifiers? posted by GTCharlie on January 16, 2008 at 01:28:55

  I forgot. the provided interstage transformer may have been spec'd just for a few mA from the 6SH7, and its very high impedance. So... changing to 5687 requires a different interstage transformer. Or you can resort to capacitor coupling. Or choke load the 5687, and grid choke the 300B, still using a capacitor to couple the driver to the final ...
  
  

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  • RE: 5687 instead of 6sh7 in interstage amplifiers? - Bambadoo 00:14:19 01/17/08 (1)
    In Reply to: RE: 5687 instead of 6sh7 in interstage amplifiers? posted by GTCharlie on January 16, 2008 at 19:39:45

    "Or choke load the 5687, and grid choke the 300B, still using a capacitor to couple the driver to the final ... "
    
    Dear GTCharlie
    I am thinking of the excact same also. Have come across some really good looking schematics I would like to try.
    
    I have a pair of AN silver 0.47uf caps that would fit perfect...
    
    But this is perhaps a bit OT regarding to this AN forum......
    
    Sincerely
    
    
    

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    • RE: 5687 instead of 6sh7 in interstage amplifiers? - GTCharlie 02:14:25 02/27/08 (0)
      In Reply to: RE: 5687 instead of 6sh7 in interstage amplifiers? posted by Bambadoo on January 17, 2008 at 00:14:19

      was revisiting previous topics ... I just found out that it's not easy looking for appropriate "commercial" chokes ... 450 - 600 Hy for your 5687 plate, at around, at least, 35mA or higher. If you're on this path, look for multi-sectioned chokes. A single wind would bring in much stray capacitance and lop off your highs. Cheers
      
      

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