Digging around in my Vibrolux Reverb and standalone Fender reverb. i found each has a Sylvania 12AT7. Both are black plates. I don't know that Sylvania had date codes but here are the markings:
1) red printing, has Sylvania triangle with 'bolt. Markings are: "DM" under that "ECA".
2) white printing, no triangle. Markings: "bg" (lower case), below that "ACB".
Any idea of the vintage of these tubes?
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