SC200 Power Amplifier: Resistor Values for ±50V DC & Distortion Graph Interpretation

Hi I have a few questions about the SC200  amplifier.

Hi I have just downloaded the last installment for the SC200 power amplifier. The article says that for lower voltage operation of +/-42V DC then changing the collector resistor of Q7 1o 15K ohms, and the collector reistors of Q6 to 4.7 Kohms is recommended. If I want to operate the amplifier from a +/- 50V DC supply then do I need to change these resistors and if so then what too.

Also there is an Audio precision distortion plot showing the distortion into 8ohms and 4 ohms at 40 and 60 watts, I assume these are measured values. I am confused what the dotted lines are for because the graphs show the measured distortion between 10 khz and 20khz actually drops off. So what are the dotted lines for???.
I am confused.

Also was the amplifier distortion measured at higher frequency of 20khz and full power. There is a graph showing the 1khz distortion into 8 and 4 ohms at full power but how does the amplifier perform at 20khz?? and full power.

Thanks
Heath

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Hi,Second attempt to reply - just lost a lot of text. I used
the Silicon Chip website graphs - the reason for the dotted line is that
this is the expected THD as the frequency is increased.
The
THD measurement is stated to have a bandwidth of 30kHz, so any harmonic
above 30kHz will be attenuated. So, at 15kHz, the 30kHz (2nd order)
harmonic will begin to be filtered out, and the 3rd order will be
significantly filtered out. As the frequency increases, the THD reduces
since the harmonics are being attenuated significantly.
Most THD measurements are made woth a 80kHz bandwidth.
Not
sure why the purple and red lines are continuous if the measurement
bandwidth is 30kHz, perhaps they changed it to 50kHz or 80kHz.
Regards,Richard.

Hi thanks for the replay. Are there any measurements for higher power levels at 20kHZ above ie 100 watts.
Regards

Hi,I do not subscribe to the magazine, so could only see the first two pages of the Australian version with the graphs shown :http://www.siliconchip.com.au/Issue/2017/March/New+SC200+Audio+Amplifier+-+Part+3?res=nonflashNo graph for 100W at 20kHz. Why not download LTSpice and simulate the circuit - LTSpice is free :http://www.linear.com/designtools/software/I would doubt that you will ever encounter an audio signal at 20kHz with a power of 100Watts.
Regards,Richard.