I determined that the pair tube was made by Mullard based on the 6CA7 compatible ball structure and date code: xf4 b8k4/xf4 B8L2 measurement value 52/50 (rejection value 30) getter with replacement box is cheap because there are burns ※ pairs are judged based on GM values measured with test machine TV-7 (Kojima Yosuke)
Accessories: replacement box