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10-10-2019, 01:16 PM
Hi liquidair
Simulations can show unexpected things for sure!
Having the screens tied to plate is not a mistake per se; rather, just shows triode mode during the mixed on/off-tubes.Certainly changing the mode between triode,UL and tetrode/pentode will highlight the different plate curve slops of these modes, which indicates the changing internal impedance of the tube according to the wiring configuration. The sim would then show varying signal currents in the 'off' tubes, which is still a little surprising.
I don't recall ever changing the mode of the 'off' tubes to hear what effect it might have on the sound, so not as thorough a test as you have done. Despite that, I don't recall hearing the distortion you report and none of my customers reported such an issue. Whether they heard it and didn't care or thought it was part of the design I don't know?
The Power Scale pot in the Standard is linear, so the voltage and current each change linearly resulting in an exponential change of power as you dial down. This is not linear to your ear. A log pot would provide a square of the log change which is faster than linear to your ear. The bias track is reasonable but not perfect but exhibits a compensating effect at low voltages, a serendipitous effect of the low internal gain of the bias regulator.
Simulations can show unexpected things for sure!
Having the screens tied to plate is not a mistake per se; rather, just shows triode mode during the mixed on/off-tubes.Certainly changing the mode between triode,UL and tetrode/pentode will highlight the different plate curve slops of these modes, which indicates the changing internal impedance of the tube according to the wiring configuration. The sim would then show varying signal currents in the 'off' tubes, which is still a little surprising.
I don't recall ever changing the mode of the 'off' tubes to hear what effect it might have on the sound, so not as thorough a test as you have done. Despite that, I don't recall hearing the distortion you report and none of my customers reported such an issue. Whether they heard it and didn't care or thought it was part of the design I don't know?
The Power Scale pot in the Standard is linear, so the voltage and current each change linearly resulting in an exponential change of power as you dial down. This is not linear to your ear. A log pot would provide a square of the log change which is faster than linear to your ear. The bias track is reasonable but not perfect but exhibits a compensating effect at low voltages, a serendipitous effect of the low internal gain of the bias regulator.
