• update... - keto 19:11:46 05/29/04 (0)
  In Reply to: 27-PP45 posted by keto on May 17, 2004 at 21:11:42:

  In this circuit, my tired but trusty Valve Art 2A3 pair are better than the 45s or TJ300Bs. Using a pair of the 20uF/600V sprague/atom electrolytic caps (from Ned's triode electronics), I've raised B+ voltage and general output stage voltage potentials to cap-input levels. I was worried that just 20uF + 20uF wouldn't be enough capacitance. Maybe the BFFC casts an inductive shadow equal to its physical one? Works fine, anyway. Mistakenly thinking I'd burned up my Pimm CCS, I had installed the 2.5K (output) cathode bias resistor. Turns out one of my solder joints was bad, and the CCS is fine. In the meantime, I think its fair to say that in a direct-coupled circuit such as this, a 2.5K Rk is a pretty good performer.

  I've been adjusting-away humm by adjusting the current of one of the input triodes (the non-signal one -- still prefer a single ended first stage, an echo of something Kurt Strain posted a long time ago), but I'm now thinking that the adjustment may just effect relative noise (via gain) of the two halves, and not really effect DC balance of the OPT primary.

  The grid choke input has a lot to do with the sound; a stable load for the source and a stable source for the load.

  Wagnerian singers and orchestra stomping around at the moment; crystal clear and miles from audible distortion. That's the latest. --keto
  
  

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