Tube Help--I'm trying to make sense of the codes on this tube.

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.