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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
oddlots
13 posts
 
I'll email Brent Jesse about this as well and let you know.
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 .
joe_appierto
81 posts
 
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.
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