Dave,
My guess is is just 200ua full scale, and likely 50mv across the terminals when at full scale.
The meter ranges are custom to the application, so long as 0-200ua criteria is met.
A 9 volt battery and a series 100K resistor should pass 90ua, or just a little less than mid scale reading.
As far as the huge slug of tubes, any chance you have any type 6HR6?
This is a pin-out equivalent to a 6BA6 but with higher gain.
Jim
Wd5JKO