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公开(公告)号：US1724972A
公开(公告)日：1929-08-20
申请号：US13213026
申请日：1926-08-28
Applicant: BELL TELEPHONE LABOR INC
Inventor： PAUL SCHWERIN , PFEIFFER JOHN G
IPC: H01J5/46
CPC classification number: H01J5/46
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