Got a new generator for the bench-an 8640B with option 004, the 1dB step attenuator. I'd like to add option 001 [the continuously variable audio oscillator] to it, and I understand option 001 is retrofittable, but as yet I have no clue where to go for parts or documentation. Even without option 001, it's still a very nice tool. 73, Brian KA9EGW