And as found with Colossus, it's power cycling
that really kills them,
so keep that to a minimum and they tend to last pretty well.
That may be a Colossus-only effect, as it did not use low power computer
tubes. The minis and subminis of the 1950s, made for computer usage, were
really not effected by power cycling. Filament burnouts on these types of
tubes are exceeding rare.
William Donzelli
aw288 at
osfn.org