> It's now foggy memory, but I'm pretty sure HP 7900A (and 7901) were using > batteries for emergency head retract.
The 7900 certainly does (there is one to go on my bench when I have some spare time). In that case it's some AA-size NiCds (not tagged ones) in those aluminium clip-in holders (Radio Shack used to sell them, I think Mouser still do). The DEC RK07 (and I assume RK06) used 8 1/2 AA cells in a pack (like 2 RK05 retract batteries in series). When I replaced those, I used 2 of the cordless telephone batteries (that have been recommended for the RK05) in series. I am told some later drives used the spindle motor as a generator when the power failed to provide the power for emergency retraction. -tony
