Offered are (4) TRIPLE MICA Sylvania 5751 Twin Triode Tubes. Two are earlier types with black plates and two are later versions with dark grey plates. The first is an early type black plate, marked 5751F, top square getter. The second is also an early black plate type this one is marked 5751WA, 562B and 312E, square top getter. The third is a dark grey plate marked 5751W1 this one has a halo type getter and big flat support rods and the fourth is marked 5751 and it has a top square getter and big flat support rods. All the tubes have good silver flashing. They test good with robust readings on the Jackson dynamic tester and they show no shorts or inter-element leakage. The readings are in the 110%/120% range for three of these and one is about 100%/100% where the good range on the Jackson is 70% to 130%.  The earlier types seldom come up for bidding nowadays. The earlier black plate tubes are likely mid 1950's vintage and the dark grey plate tubes are later.  Pick up the (4) good, tested, US Made tubes for your best gear or for work upcoming and for a great price!. Mouse over the photo images to zoom in. NO RESERVE!! Thanks for looking.