My particular 101D Cabernet unit has not a small noise from the power supply. The HT lines had about 20mV p-p ripple and the DHT filament DC supplies had the same amount. It was a scary to work on the power supply so I decided to work on the main unit. Fortunately after removing the remote control PCB which I never use, it has space for me to put in a 5H choke and a 80uF film cap on each of the HT lines. I made use of the empty cans and put in a 18mH choke and 10000uF for the DC filament supplies. The circuit seems to be a constant current supply for filament with a LM317 which had about 20mVp-p ripple. After the mod which does not touch the signal circuit, I cannot measure the ripples with my equipment. The 2nd, 3rd, etc harmonics of the power supply noise are all gone. The SNR improved by 16dB and I cannot barely hear the annoying humming noise from the speakers. There's still a stubborn 60Hz noise from the FFT which I suspect is coming from the cathode which is from another DC regulator. But now I'm quite happy with the results.
Like @jslateiv said the sweet spot is around 8-10 o'clock of the volume knob to get minimal distortion, mostly consisting of 2nd harmonics. The gain I got was about -6dB to 0dB.
Like @jslateiv said the sweet spot is around 8-10 o'clock of the volume knob to get minimal distortion, mostly consisting of 2nd harmonics. The gain I got was about -6dB to 0dB.