How do I bias the tubes in my amp?

Just bought a Golden Tube Audio SE-40 and sat down to bias the tubes so I could listed to my first tube setup and found that my Voltmeter only goes up to 400mV. The tubes need to be set at 640 - 650mV. I went to Radio Shack to buy a new meter and all of the meters they had cut off at 400mV. I'm sure there is a simple answer to this but I don't have it. Can anyone help me by telling me how to do this, or where to get a better meter?
Thanks,
Rick