have had to replace several of these myself on my altair and on my IMSAI. 7406 seems to make a better replacement as it can take higher voltages Hi I've notice these as being a common failure item, as well. I don't think it is the voltage that is killing them. It is more likely a timing overlap issue with other parts driving the bus and stressing these parts. One might consider adding some resistors in series ( small value ) to limit the current when a tristate drive also drives the bus at the same time as the '05 is active ( driving low ). I would suspect that something in the order of 15 ohms would be enough to protect the '05's and still drive a solid '0' onto the bus lines. There is no reason that any voltage issue should cause problems with these parts. Later Dwight