Do any of you 'know' for sure which batches of the Ampex reel to reel audio tape had the problem of gumming up the heads on the tape deck? I have two new 3,600 foot ten inch reels of back coated, studio quality tape here, number 373173111. This was expensive when purchased in the late seventies or early eighties. Is it the good stuff or the stuff that messed up machines? Thanks. Duane Fischer, W8DBF