They crank those heads unbelievably tight to get that snappy sound and you often find black kevlar heads cranked ultra tight. (tighter than unbelievably tight) Make sure the lug threads are clean and turn easily under pressure. Be careful using a modern kevlar head and tension because the pressures that are usually used on them may be more than anticipated by the designer of a vintage snare and could hurt the drum. I would try to stay with whatever heads and tension were used during that time period.Some say "tighten the top head until it chokes, back off and creep back to just shy of choking.....but with the warning above in mind.