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The etched code is the way to determine exactly what you have.
Gf is the tube type, in this case a 12AU7
2 is the change code which tells you what revision of the tube you have, like a model number.
The second row of codes tell you the factory it was made at and the date it was made.
B means the Mullard factory at Blackburn, England.
5 is the year of manufacture. Since these are orange label, which were made in the late 60s and the 70s, the year is 1975. If the labels had been white, I would say 1965.
J is the month, 10th letter of the alphabet is the 10th month, October.
2 is the week of the month.
Phillips was a Dutch conglomerate that owned many tube brands such as Mullard, Amperex, Siemens, Valvo and many others. Tubes made in one factory were often labelled with another factory’s brand if an order needed to be filled or whatever. Phillips also sold tubes to independent distributors like Los Gatos and National who put their own labels on them. Other manufacturers like Telefunken and RCA had their own ways of coding tubes.
Phillips tube codes can be found here:
Another good resource for identifying NOS tubes is the Tubemonger picture library, which contains pictures of many, many NOS tubes:
You’re both welcome.
jbhiller, you can also see the date Amperex painted their label on below the 12AU7A, 76-48, meaning the 48th week of 1976. The labels were usually painted on a while after the tube was made, so this verifies that the tube was made in Oct. 75. Usually Phillips companies didn’t paint a date code on their tubes, but obviously they sometimes did.
The 2 change code means that the construction of the tube is the same as those made in the 60s. I know that Mullard made Gf 2s in the mid 60s, so those are some nice tubes you have there. They are in beautiful condition.
Everybody's welcome. I'm glad to have a chance to put my tube knowledge to use. Another good resource is Brent Jessee's web site:
He has the Telefunken tube codes there as well as explanations of all the tube varieties that can be substituted for a particular tube like the 12AU7. He also gives opinions on the sound of various tubes, some pretty specific, some general. These opinions aren't gospel. You never really know how a tube will sound in your system until you plug it in and listen. He has a good reputation as a tube dealer and he'll help you find what you want if you give him a call.