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.
Who made the tubes?
I have a pair of 12au7's labeled National and made in Great Britain. Are these Mullard's?
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