IBM vacuum tubes

[Guy N.]

On Wed, 2020-06-17 at 13:24 -0400, William Donzelli via cctalk wrote: 
> 5965 is a computer rated 12AV7 with better balanced cutoff
> characteristics, but generally worse for noise.

Darn.  "Worse for noise" probably means I won't find audio nirvana
trying these in any of my amps.  And there's a good chance they're worn
out anyway (one of my theories is that these are tubes that were
undergoing reliability testing or failure analysis).