• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

I can’t find a wire description for this transformer

I have a Vintage Baldwin Power Transformer #512-19205 and found this description on the net but can’t find any labeling of what wire is what.

120v primary
710v center tap

Do you not have a VOM or multimeter of some kind? The high voltage will be the highest resistance reading. (red?) The two low voltages will be the lowest. And the 120V primary will be somewhere in the middle. (black?) To verify start up with a variac and measure voltage output. Don't have any of these items? After all your years of building electronics you should have.
Likely black = primary.
Green = 6.3 volt heater
Blue = maybe bias or some other heater?
Other side is likely center tapped plate. Yellow stripe = center.
Would need weight/size to guess how much power overall. DC resistance can help guess current.
Also remember when measuring DC resistance that when disconnecting there can be some flyback voltage, You do not want to be touching them.

Could be 120v, maybe a dim bulb test across the 120v/black wires will tell if 120v seems right.