my Data General Nova 4/X, disk woes continue

I hope they are not in any timing circuits. Another way to really shoot ones foot is change all logic and any analog stuff or worse digital used as analog. Newer or older parts often will behave different and at 10mhz that was high speed then. There be serpents and devils lurking there. This tells me you've not looked at the cause only apparent problems that may not be relevent. OK, the drive uses the same CART as a DEC RL01/02 and the base design is a CDC creation if memory serves. DEC nor DG designed the beast. There are two things to pay attention to. Servo amps for the positioner they are analog and can drift. They must be set up at TEMP. If I remember that varient of the drive also had embedded servo information for the head position controls. The second is the read/write electronics have a PLL for read clock recovery. If thats not set up right it will drift outside the lock in range and start tossing errors. It also must be setup at working TEMP. The PLL is to track drive speed errors and irregularities in position and bit shifting. Did you mean "two state amp" or "two stage amp"? Likely it's not an amp problem, a quick look with any old scope could check that as it warms up. Early disk systems like that seem to have their fair share of green, blue or white and red wires. Grean being factory changes, white or blue were often depot repair and red field implemented. I'd not be too concerned if it worked before it should again. Allison