• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Audio research LS2 hiss and hum... need help


Just buyed a second hand LS2 and when i plug it on my system, i heard hum and hiss. Hum is present when volume knob is low, disappear when the volume knob is about 1/3 coarse and then increase for the last of the coarse... Hum is present on all sources (also in Direct in) and disappear when mute key is on.
Hiss appear and disappear and sound like old phone internet modem...

First off all, i have change the tube with a NOS Philips ECC88... no change

I have recap all the HT capacitors... no change, all voltage are ok (just a little bit more).

Does anybody have same issue or can help me to fix it ?

By the way, sorry for my bad english. It come from a French guy...