Congrats on your "new" Sansui. I just added one to my collection and love it.
On antennas, first, free and easy, try hooking the wire to the other 300 screw just to see if it gets any better. Second, cheap and easy although not DIY, get a $4 folded dipole from Radio Shack. It's terminated in 2 little spades that you hook up to both 300 ohm taps. Even though tacked to a wall high as possible is best, you can hang it down the back and stretch it out on the floor as far as you allow. You may be surprised.
On antennas, first, free and easy, try hooking the wire to the other 300 screw just to see if it gets any better. Second, cheap and easy although not DIY, get a $4 folded dipole from Radio Shack. It's terminated in 2 little spades that you hook up to both 300 ohm taps. Even though tacked to a wall high as possible is best, you can hang it down the back and stretch it out on the floor as far as you allow. You may be surprised.