Right Channel Noise in KT88

1. Output Tube problem....
if not
2. Check the Bias of the tube, if one of the transformer is not, then the bias is too high and the tube may end up have problem.  The high bias may be one of the resistor that give bias to the Grid is not good.
Do you know how to measure the bias of the output tube ?

For auto bais , KT88 第八腳會接一支 數百 ohms 的電阻落地，流請check 是否這支電阻有事。亦有可能是接第四腳落地的電阻有問題。

Look like that this is not auto bias, from the photo, it had a trimer which provide the grid with a negative voltage. It is better to draw the circuit and measure the voltage on the grid of the kt88

Yes, the pot should adjusting the negative votlage to the grip and also I see there is 1 6.8 ohms resistor for both KT88, if they are using auto bias, this resistor should be a few hundred ohms. This resistors are connected to Ground so it should be fixed bias.