Amperex 6DJ8 tube construction

Left one is Amperex Holland made and a great tube, the one on the right is a Matsushita made on same tooling as Mullard but a different tube.
Always check the etched codes at bottom of tube to identify the origin.

What is common in Dutch made tubes, including Mullard, Amperex USA, French, Belgian, Indian and so on, and German tubes like Siemens and Halske, Telefunken (same tooling and construction for early Teslas also) is the ridged shield - a plate with two ridges 180 deg apart.
Sylvania, Tungsram (Hungary) had a plate shield with no ridges.
All for ecc88 family of tubes.

Joe's Tube Lore refers to the A frame type but that tube by construction does not have the ususal type of shield as earlier tubes (like the one on left picture).