Sorry, I was out of the office and missed this thread until now.
The 0-1800 and 0-1500 pyrometers do NOT use the same amplifier boxes. They look very similar from the outside, but they are different internally.
If you are just swapping parts to determine which part is bad, the amplifier boxes will work with the different range gauge, but they would not be accurate.
Regards,
Michael Pliska