XPost: sci.electronics.repair   
   From: legg@nospam.magma.ca   
      
   On Mon, 30 Jul 2012 13:01:32 -0500, legg  wrote:   
      
      
   Anecdotal info suggests that ECC85 (6AQ8) was developed and marketed   
   after ECC81/12AT7, and that ECC85 was developed specifically for VHF   
   input/oscillator combinations. An improved inter-device screen   
   supposedly reduced oscillator stage radiation. This isn't an   
   input/oscillator schematic application, in any event.Not sure what   
   6BK7A does that's special.   
      
   When converting from 6BK7 to 6AQ8 or 12AT7, the cathode bias resistor   
   in self-bias is supposed to increase from 56 to 200R, to maintain   
   similar plate currents.   
      
   Looks like this is actually a later revision.   
      
   Just wish they'd documented the changes.   
      
   RL   
      
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