XPost: sci.electronics.design   
   From: tauno.voipio@notused.fi.invalid   
      
   On 28.12.18 10:45, upsidedown@downunder.com wrote:   
   > On Thu, 27 Dec 2018 21:11:35 -0600, tubeguy@myshop.com wrote:   
   >   
   >> I'm not intending on building this, but it's interesting and makes me   
   >> wonder if someone could use EIGHT 6L6 tubes, or TEN?   
   >> (Of course adding more tubes mean bigger audio output transformers and   
   >> heftier power supplies.   
   >   
   > Tubes may age at different rates, so the characteristics might be   
   > quite different after a long time. It might not make sense to replace   
   > a single (failed) tube and you may have to replace the whole set of   
   > tubes with new tubes preferably from the same manufacturing batch.   
   > This can be quite expensive :-)   
      
      
   In the 1960's, I made a guitar amplifier with six EL500's. The tubes   
   are not characterized for linear use, and they were not matched in   
   any way. Each tube had an own cathode resistor, and there was no   
   evidence of any overload from unbalanced operation.   
      
   The tubes had a tendency of parasitic oscillation, so I added a   
   ferrite bead on the control grids and an inductor-resistor parallel   
   combination on each plate (for constructions, see nearest ham handbook).   
      
   --   
      
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