Are you reading voltage off a cathode bias resistor? What's the current running through each side? I usually set the initial bias at 35mA for each 6L6, el34's or 6550's somewhat higher (sometimes as high as 75mA per tube, which gets hot!), but then I adjust by tone. As long as you don't exceed the max dissipation wattage of the tube, your fingers aren't getting burnt when you touch the front, and the amp doesn't smell from the plastic melting off the wires, I think you are probably okay. But if a customer says the amp is too hot, I would bring the current down until he's happy. If his tone suffers, you could always tell him his bias is set too cold...and start charging him to re-bias.