Are you sure it's a smooth grey plate? Those letter codes in place of the year code indicate that it's a late vintage black plate circa 1959/1960 just before they went to the smooth grey plates. It might be the first grey plate version. Who knows? I have a number of black plates with those letter codes myself.
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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