So I found a guy with a military bulk pack of GE Canada tall bottle 12SX7s all made the first week of 1970, two made the 38th week 1966, and one made the 10th week of 1968. I am keeping a bunch for my 1625 based tube amp and am going to sell the rest. The 12SX7 was a special 12SN7 used in certain airplanes (allegedly the U-2, but I have no idea if that is true). Basically, what it means to you is that it is a more highly matched 12SN7 and, in most applications, can slot in for a 6SN7. On the ones of these that I have measured, the sides are within 0050Gma of eachother (on my Hickock).
I have 6 pairs to sell, of which I can make 2 matched quads (based on my Hickoks' readings). The quads have all 8 sides matching within 0150Gma of eachother all around.
I am not trying to make a profit, but just want to break even. I will sell quads for $105 shipped, pairs for $55 shipped, and the single from 1968 for $30 shipped. Will consider trades for quads of 12SX7/12SN7 tubes I have not tried.
