What you say certainly describes the RK05, lots of 8" floppy drives with AC-drive motors and belts, and many other 14" disk drives, but I'm now 99.44% certain that there's a servo loop for motor speed regulation in a RL02 and that it's not tied to having a mathematical relationship of pulley sizes or the AC line frequency. In fact, my "RL01/RL02 Disk Drive Maintenance Course" textbook says: The circuits controlling the drive motor in line are located on two modules. The drive logic module decodes the speed of the rotating spindle and sends the signals to the AC servo module which controls the drive motor's duty cycle. The disk speed control portion of the DLM monitors the sector pulse that is created from the reluctance pick-up and shaped by the circults on page DL6. This shaped sector pulse, called sector detect, and the clock from the interface logic are used by the counting logic to determine how much time is elapsing between sector pulses. The result is a signal called Control Speed-up, which is sensed by the AC servo module. When active, it increases the duty cycle of the drive motor from 20% to 60%, speeding up the cartridge. If the disk is within the speed limits., Control Speed-up is negated, allowing the drive motor to run at a 20% duty cycle. This indicates that the master clock setting the drive rotation rate comes from the interface board in the Q-bus/Unibus/Omnibus (I believe this is in turn derived from a crystal oscillator), and that it is not directly tied to the AC line frequency. Indeed, if you put a not-RL01 or not-RL02 pack in a RL drive and try to spin it up, the fact that the sector gaps aren't present in the same number means that it'll spin up to a different speed than if you have a real RL pack in the drive. There may be a separate "50Hz" RL drive variant, but I've not seen any indication of its existence here in North America, in parts lists, user's manauls, or in maintenance guides. I'm sure some of our more international members will have better information than I do. -- Tim Shoppa Email: shoppa(a)trailing-edge.com Trailing Edge Technology WWW: http://www.trailing-edge.com/ 7328 Bradley Blvd Voice: 301-767-5917 Bethesda, MD, USA 20817 Fax: 301-767-5927