Just as a point of information, Tung-Sol (the company that invented the 6550), introduced the first version of the 6550 in 1955 with the single getter black plate.
MFY Tungsol 6550 tube old versions
In my ARC REF 3 I 'm using a Tungsol 6550 tube with the following code written on the metal base 322NU 3 , it is a smooth grey plate , without holes in the plate .I know 322 is the factorycode of Tungsol and normally the 322 is followed by eq 63=year 45=week 3= shift ?.But I have seen also 322HN-3 and RM-3 .Is there any list of these codes ?
Any help would be wonderfull
Any help would be wonderfull
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