Suggestions for DTV booster amp?

[toxcrusadr]

Short version: Looking for a booster amp because my convertor box isn't finding enough signal on the cable to work.

Long version: we have cable using a digital cable box (Mediacom) upstairs on our flat screen TV. Downstairs we have the old 35" Mitsu beast, still running after 17 yrs. and 2 minor repairs.

I know the cable has a group of channels (not all of them) accessible even before the cable box. We can watch them on our bedroom LCD w/o a cable box. I ran a line to the old Mitsu and figured I could insert a DTV convertor box and get those stations. It can't find a single station. I can hook up an antenna and get a couple over the air so I know the box works, more or less.

I know these boxes suck, do I need a booster amp? I don't wanna spring for $10/mo for another Mediacom box.