Identifying KT90 tube types
I've got some Ei KT90's and trying to identify the types. These photos show two of them. They have different boxes, though I'm not sure that matters. These two look quite similar, with the square "patch". I also have two with a circle on the "patch" (does that mean they are type IV?). The two with the square patches are constructed with the patch on opposite sides. The one on the right has more visible spot welds. The one on the left has white lettering, the one on the right, no lettering (though it might have rubbed off).
Anyone familiar enough to help?
(I'm not familiar with links to photos here, so I hope this works)........