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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
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.
oddlots
13 posts
 
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.
jedinite24's avatar
jedinite24
1,503 posts
 
Have you tried contacting Brent Jessee or Jim McShane? Those are to NOS tube experts. They should be able to help you.
xti16
1,525 posts
 
Oddlots - I had some smooth grey plates with letters in place of the year. I got them from Brent Jessee but traded them a while back.
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