Vacuum tube encryption arrangement looks easy, it is very difficult, the main problem is a liner tube hole connection is too narrow after the processing difficulty, easy deformation.
真空管加密排列看起来容易，做起来是很难的，主要问题一是内胆管孔连接处过窄后加工难度大，极易变形。
3
If a triaxial vacuum feedthrough is unavailable, a metal safety shield should be built around the isolated BNC connection (Figure 4-18).