IBM vacuum tubes

[Guy N.]

While going through my assortment of old vacuum tubes looking for audio
treasures, I found a handful of IBM branded ones.  Mostly 5965, but
there's one 5963 mixed in.

These are dual triodes with the same pinout as common small-signal audio
tubes such as 12AX7/7025/ECC83, but characteristics closer to 12AT7 or
12AU7.  My RCA Receiving Tube Manual says they're designed to withstand
being held in cutoff for long periods of time, and mentions digital
applications.

Anyone know what kind of IBM machine these would have been used in?