Being 50 miles away, you most likely could use a preamp. Dont buy a distribtion amp. Buy one that is meant to go up at the antenna. A Channel Master 7777 is highly rated.
http://www.solidsignal.com/prod_display.asp?PROD=ANC7777
The key spec being noise figure. The lower the better.
But you could also be having multipath problems. If you tune in analog stations do you see any ghosting. If so, you have multipath and a preamp isnt going to help. You just might need to re-aim the antenna.
Also, hows your coax cable? Is it the thin RG59? If so, it has higher losses than the thicker RG6. Replace it and it will help immensely. What shape are the connectors in? Can you grab them and pull them off by hand? If so, time to replace them with some good comression connectors. Basically, you need to whip the entire antenna system into shape to cut down on signal eating losses.
I live 70 miles away from the transmitters and I have no problem receiving ATSC.
-dickm