The really old Andrew machines used a conventional (for the time) RC
relaxation circuit, so I'm not sure why it would be especially good for
cutting diamond. Is this one of the granite-base machines with the moving
head?

Yes. According to Mike, there were three major generations of wire burn
circuits on the Charmilles Andrew machines, the focus of technology at the
time. The machine I have was made just before pulling the Andrew name off
the machine. Again, according to Mike, the next focus was making the burn
circuit more user friendly by computerizing the control of the burn circuit.
This worked, but you actually lost ability to do the tuff stuff if you knew
the machines well.

Karl