The good old 74LS series, once the staple of logic design, is all but forgotten, except that there might still be a lot lying around. These parts are only specified at 5V +/-5%. Can they run on 3.3V supply? When they run on 5V supply, their output is about 3.6V which is safe for the 3.3V logic. And they can still operate at 3.3V, the output is about 2V, which is still acceptable for 3.3V logic. Their inputs are 5V tolerant.
