My friend got a KT88 power amp that gives off "ssss....sss" noise on the right channel. The funny thing is, the noise is random. Sometimes you hear it when you start it up, sometimes it appears when the machine is turned on for 1 hour or more.
What could have caused the problem? Swapped the tubes already, still no good.
AND the right channel OUTPUT transformer is really HOT compared with the LEFT one.
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 ?
My colleague used different tubes already (e.g. swap left right) and the problem is still consistent in the Right Channel. So probably it is not the tube.
I know how to measure BIAS for my 6L6 as there is a hole in the chasis. For this CARY KT-88, I have no idea how it can be done.
Should I post some photos here so that you can give me more advice?
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.