Generously grease an 8x8-inch cake pan. In a 2-quart saucepan, mix the sugar, water, corn syrup and salt until well combined. Stirring with a wooden spoon, bring the batch to a full boil over high heat. When the mixture starts to boil, cover the saucepan and allow to boil for 1 minute. Remove the cover and wash down the sides of the pan with a pastry brush dipped in hot water. Clip a candy thermometer onto the side of the pan and cook at high heat, 5 to 8 minutes or until mixture reaches 240 degrees. Remove the saucepan from the heat and without removing the thermometer, allow mixture to cool to 150 degrees and then add the preserves. Beat with an electric mixer on low speed for 4 minutes. Pour the mixture into the cake pan. Allow to cool at room temperature for 45 minutes, then with a wet knife, score the top into 1-inch squares. Refrigerate for 1 hour. Remove from the refrigerator and place a piece of wax paper on top of the fudge. Turn the pan upside down onto to a work surface to remove fudge from pan. Turn fudge right-side up and with a wet knife, cut the fudge into 1-inch pieces, wiping the blade between each cut to insure clean slices. Wrap and store pieces in the refrigerator.