{Collins} Fun with 6146 markings

Dear collegues
we all know about the fine points using 6146 tubes in S-Line equipment. Just to add to the confusion I'd like to report that I have here two tubes marked as follows:
a) etched into the glass envelope: "6146", "B", "U.S.A." and a group of dots.
b) silk screened on in orange color: "Amperex" with logo, "6146A", date code 83-18.
Any more of these things around causing problems? Have not yet bothered to find out what they really are, B's perhaps?
Best regards and thanks for the bandwidth,
Ulrich Fierz  hb9aik - vk6bqd

Ulrich N Fierz
Telecommunication Engineering Services
CH-8044 Zurich

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