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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
128x128hansk46

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hansk46 OP
122 posts
 
At first thank you Jedinite24 for JimMcShane 's address ,I sent him an Email , even to tubemuseum and newsensor , just have to wait , and yes Oddlots , I 'm sure it is a smooth grey plate without holes , and looking at the foto 's and description of Tubeworld it could be from 1960 to 1963 , but still want to know the meaning of the code
hansk46's avatar
hansk46 OP
122 posts
 
Up until now NO info about the code 's , so we have to look at the tube itself and with the help of the info supplied by TUBEWORLD we can see :
Black plates,1-2-3 getters 1950-1960
Smooth gray plates,all without holes 1960-1963
Gray plates with holes 1963-1970
If supplied with the 322 63=year 45=week 3=shift you have a refference .
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