After a fuel stop, I taxied my '64 C (manual gear) onto the active after my run-up.   I was going maybe 3-4mph, and all of a sudden, the nose gear collapsed, followed by both mains about a second later.  After the initial shock of what had just happened, I quickly hit the master switch off, shut off the fuel, and exited the aircraft.  The J-bar never moved out of the block.  Fortunately, there was an A&P on the field, along with a group of other very nice folks who helped me put the plane on