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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
hansk46

Showing 2 responses by joe_appierto

joe_appierto
81 posts
 
I know what you're talking about as I have both the numeric and alphanumeric tube codes on vintage Tung-Sol tubes but I've never seen a list to break down the year and week of production.

I'd be interested myself if anyone is aware of such a list.
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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