01-09-2016, 08:10 AM
Hi Trevor, at low listening levels it probably will stay in class A. You could afford to reduce the anode current further to maybe 75 or even 50mA, cathode resistor of 680 - 1k and still not encounter crossover distortion. This would reduce the heating bills further? . With an output of maybe 20 watts max the 6550's are under used and as you say the fixed bias was unnecessary at this low power.
The Wialliamson amp seems to be based around correctly wound transformers where the layers of primary and secondary are interleaved to give equalised coupling over the whole winding. I've seen some interpretations where the circuit topology can change from long tailed pair phase splitters to concertinas. I personally prefer the long tailed pair for linearity. The other point of the design was distributed negative feedback around each stage with a smaller amount of overall feedback applied. Too much overall feedback will invoke phase errors at some frequency and should be there only to account for speaker damping.
Dave.
The Wialliamson amp seems to be based around correctly wound transformers where the layers of primary and secondary are interleaved to give equalised coupling over the whole winding. I've seen some interpretations where the circuit topology can change from long tailed pair phase splitters to concertinas. I personally prefer the long tailed pair for linearity. The other point of the design was distributed negative feedback around each stage with a smaller amount of overall feedback applied. Too much overall feedback will invoke phase errors at some frequency and should be there only to account for speaker damping.
Dave.
