Phil, yes, it's one of the SG tubes, really nice, I think these are new, not rebuilt or just regunned.
This one took the B&K meter to about 98 out of 100 on the scale.
Mine had the warranty card in the box, dated Feb 21 1966, does yours have a date?
I would expect them to be similar.
Should we send in the warranty cards?
They'll wind up here at 437 S. Illinois St Indianapolis:
http://g.co/maps/xyyxn Now a "Gentlemans Club"