Why does my tube amplifier hum after changing the power tubes?

This is often due to an incorrect bias setting of the power tubes. If adjustment options are available, the bias must be adjusted. However, it can also be caused by the hum balance potentiometer, which has to be set to the minimum hum position when changing the power tubes. Another possible cause can be the tube socket. If the contact is not clean, this can also lead to deviations in parameters and even overheating.