Um... if you have a meter to measure the bias voltage, can't you measure the plate voltage with it? And, if you're not too sure about poking around in your amp to measure things like that, don't you think it might be worth the $$$ to have a tech bias it for you, since the amps run over $1K? Not coming down on you, but it seems to me that it would be a safer way to protect your investment.
The paperwork with the amp says to bias from 40 -52. there are bias probe ports built into the amp, so it's pretty easy. I will probably have a tech look at the amp, I've got a respected one in my area.
I tried installing a KT-66 HP but the range of the Bias pot would only bring it down to 58, so I did't use it. It was a 5 on GT's hardness scale if that is relevant.