Does your amp have bias trim controls? Sounds like the right channel bias is set too high.
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Your amp most likely has cathode-bias whereby the cathodes are connected to ground via a fairly large value resistor. The current flowing through that resistor causes a voltage drop which the grid "sees" as a negative voltage relative to the cathode. This is the bias voltage. If the value of this resistor is lower than it should be, the output tubes will run at a higher current.
I agree with the suggestion to take the amp back to Vu, but if you don't live in the DC area any competent tech should be able to figure this out.