Field wound DC Servo

Hi All,

I am working on a large milling machine that has field wound DC servos
fitted. I am wondering if there is some way to figure out what
voltage to run through the fields.
I want to be able to run a constant voltage through the fields and run
the armature through the servo amp, but there is no info on the field
voltage or current draw. If I run these servos this way will there be
trouble with the servos getting excessivly hot - this machine will be
running pretty well continually for 6 days a week.
Any help will be greatly appreciated.

Regards
Andrew