This is serial number 1637.  It has been restored by Howard Mills.  Although this isn't such a great photo, you can see that it has been repainted and re-lettered and appears just about as new.  Click here to see the complete specifications of the 75A4.

75A-4 Summary
Introduction Date: 1955
Price in 1955: $595
Price in 1958 $695
Size:  10-1/2" high x 17-1/4" wide x 15-1/2" deep.
Weight:  35 pounds.
Tube List: 0A2 (1), 5Y3GT (1), 6AL5 (4), 6AQ5 (1), 6BA6 (8), 6BA7 (2), 6DC6 (1), 12AT7 (3), 12AU7 (1).
* Note: Tube variations depend on vintage.

Complete Specs of the 75A4