Mine had the Fetron until a year or so ago. With the help of Boogiebabies and a lot of work on my own, I was able to convert mine to the 12AX7. There was only a mention of the fetron in the papers and it also stated you could just replace it with the 12AX7 which isn't really true. There are several things that have to be done to make it sound good.
The schematic that came with my amp wasn't accurate either. Turns out I mine was built right at the beginning of the MarkII and actually had that amps power supply.
Are you trying to convert a fetron to a 12AX7?