Well after four years...a thread resurrection.
My current amp that runs 6V6's I think is biased upward of 75% to 80% of design center max plate dissipation. What set that bias point was (of course) the screen voltage chosen, which was chosen to properly load the output stage given the primary impedance of the transformers. But also, because that's where the lowest THD was measured at full power output. It's a bit of a different animal, being pentode connected and using Dave Gillespie's EFB output stage regulator. This amp uses Heathkit AA-100 iron, and is easily the best sounding amp I have scratch built to date. I'm confident that what makes that amp great is the output stage regulator and the output transformers, or more specifically, the HF extension offered in those output transformers.
Primo, it would have been whatever bias setting would cause about 60% plate dissipation. (from design center max). I don't have those notes any longer to know exactly what that value was. No particular reason for the 60% plate dissipation...not too hot, not too cold.Hi Kev, nice work on the amp! What bias do you run the 6v6?
My current amp that runs 6V6's I think is biased upward of 75% to 80% of design center max plate dissipation. What set that bias point was (of course) the screen voltage chosen, which was chosen to properly load the output stage given the primary impedance of the transformers. But also, because that's where the lowest THD was measured at full power output. It's a bit of a different animal, being pentode connected and using Dave Gillespie's EFB output stage regulator. This amp uses Heathkit AA-100 iron, and is easily the best sounding amp I have scratch built to date. I'm confident that what makes that amp great is the output stage regulator and the output transformers, or more specifically, the HF extension offered in those output transformers.
Don't know. I don't have an FFT analyzer. The feedback tap from the screen is actually not a new idea. Dynaco used it in their Mark III, and probably others. I kinda copied it from that. Works very well on some transformers in taming the winding resonances and not well at all on better wound iron with very little winding resonance.Interesting you have feedback from the screen. I wonder since you feedback from one side only, it might increase even harmonics and give it a more present sound.