Vintage  RCA  7591A output tube.  Tests excellent  on my Triplett 3444, at 7500 Gm where min is 4600 Gm.  Construction is grey plates with a ring getter. I recently sold 7 other 7591A tubes, of all those tubes this one read the  the strongest! Lot code is "DN", tube has the RCA "meatball" logo and the orange print. . Labelling is in very good shape, base and tube glass are in good shape. No cracks or loose base, no flakes, no broken octal pin. comes with RCA box shown in last picture. The box is worn and showing signs of shelfwear, but the tube is much cleaner.  I get lots of compliments on tube quality , accurate description, good packaging , and fast shipment, see my feedback if interested. Good luck bidding!