Hi Ejman
For me I didn't like seeing the red lights flicker a lot on the 502P. When I was striving for the exact 500MV there wre times I saw the lights really flicker a lot. That and I was under the impression for the amp to sound the best the power tubes should be biased at 500mv or a little above.
To your question about differences in sound when the tubes were biased above 550MV. I didn't notice any differences but I didn't have my power tubes biased above 550MV for very long. I had the 502P on for over and hour and played a couple of songs. Then checked the bias and it was 700MV on the tubes.
How this happened was I was power tube rolling between NOS 6550 tubes and Tung Sol KT120 tubes. I thought I had dialed down the bias enough before making the changes. I make the switch and then check the bias later and it was very very high.
So please be careful when you are power tube rolling and don't make the mistakes I did.
Lastly when I called Jolida to discuss the 502P they told me if you wanted to really make audible sound differences with the amp was to roll 12AX7 tubes.
For me I didn't like seeing the red lights flicker a lot on the 502P. When I was striving for the exact 500MV there wre times I saw the lights really flicker a lot. That and I was under the impression for the amp to sound the best the power tubes should be biased at 500mv or a little above.
To your question about differences in sound when the tubes were biased above 550MV. I didn't notice any differences but I didn't have my power tubes biased above 550MV for very long. I had the 502P on for over and hour and played a couple of songs. Then checked the bias and it was 700MV on the tubes.
How this happened was I was power tube rolling between NOS 6550 tubes and Tung Sol KT120 tubes. I thought I had dialed down the bias enough before making the changes. I make the switch and then check the bias later and it was very very high.
So please be careful when you are power tube rolling and don't make the mistakes I did.
Lastly when I called Jolida to discuss the 502P they told me if you wanted to really make audible sound differences with the amp was to roll 12AX7 tubes.