Ah, but if you felt any vibration turning it, the bearings are shot, or as in the case of mine on the 220, the stator or rotor are bad and making contact. May only give a small "tight" feeling at one point in a revolution.
It should spin freely when you give it a twist, and keep spinning for a couple revolutions. If it stops as soon as you let go, the bearings are bad. ANY sound above a whisper of the brushes sliding on smooth slip rings means something is amiss.
Put the belt back on and get a stick long enough to put up next to your ear and safely touch the alternator. Start the car, put the stick on the alternator, then put the other end up to your ear (this is a mechanics stethascope, dirt cheap version). Anything louder that a faint sizzling or whirring sound means bad bearings. Knocking or clattering means stator/rotor interference.
If it's loud enough to hear without the stethescope, get a new alternator.
If it has bad bearings, or internal interference (or something stuck in it), the drag will eat the belt up pretty fast.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!