Details
Used old stock 9 pin miniature twin triode. Various brands. ECC81 is the European designation.
NSN/FSN = 5960000781680, 5960001667662, 5960004453238, 5960005072099, 5960005575417, 5960006155584, 5960007627382, 5960008466619, 5960009566498
HP/Agilent Number = 1932-0027, 1932-0028, 1932-0042, 1932-0045, 1932-0058, 1932-0069, 5080-7343, 5080-7336
Tektronix Number = 154-0039-00, 154-0205-00