Yeah I did swapped tube from left to right, and switched different tube set. the left mono channel seems total fine, but right channel is in bad
shape. used since 2009, earler version with per amp model. it's been a while, feel maybe overheat burn out some resistor on right mono.
Finally I open it up. very interesting is as i know inside the amp should have
2 Gold 20W100RJ,
1 Gold 20w430RJ on each channel,
but mine is 2 Gold 20W100RJ, and 1 sliver 20w430RJ in each channel.
I'm wondering if it is possible the gold 20w430RJ heat up too much then become sliver color......if so, then my left channel may goes out soon due to it change the color to sliver already. no idea but very Curious how this open?