bobthebanana:
Ok, I drew up and attached a schematic. I've also noticed that if all of the A and B inputs are pulled low my current draw is ~150mA and when they're high it gets up to ~300mA!
The pull downs are clearly responsible for the difference between those two figures (why have pull downs at all? This is an odd way to use TTL)
The large value of the supply current makes me think ether the chip is broken or its a 74S181 rather than a 74LS181...