National bought tubes from many manufacturers. They could be Mullard, Brimar, or Ediswan. Click on, "images" here; (http://www.mullardtubes.com/Mullard-ECC82-12AU7-CV4003/?ID=0&ProductID=153) or, "more detailed photos" here: (http://www.tubeaudioproducts.com/Mullard-Brimar/ProductDetail.aspx?CatID=65&ProductID=227#), and compare the construction to what you have. At least you'll know if it's a Mullard or Brimar. There are two clear images of the Mullard's construction. Use your keyboard's right direction button to get to the second pic, on the Mullards.