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公开(公告)号：US1980596A
公开(公告)日：1934-11-13
申请号：US52177931
申请日：1931-03-11
Applicant: HYGRADE SYLVANIA CORP
Inventor： POOR WALTER E
IPC: H01J21/20
CPC classification number: H01J21/20 , H01J2893/003
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