Wilson made many rackets with the Jack Kramer name attached to it.
Many were fine quality rackets but a few were made for big department stores. Does the racket have a stamp inside the hoop saying Belgium or Made in Belgium?
If so, than it's made by Donnay and likely to be of lesser quality. Original strings can also tell you what overall quality the racket is, if it's white with black, red or blue spiral it's not the best frame I'm afraid.
2x MAX 200G PRO, Nat.Gut/Ferry Force Super Touch at 58 lbs.