[Amps] Step-start and 3-500Z filament life

[Bill W5WVO]

I understand why turning a tube's filaments off and on repeatedly
shortens the tube's useful life. However, I'm not clear about the
effects of doing this when a step-start circuit is included (as in
the Harbaugh step-start kit, which I have installed in my
6m-converted SB-220). How much difference does this really make in
the life of the tubes? I would like to stop worrying about the
tubes degrading due to filament deterioration. The tubes are brand
new RF Parts 3-500ZGs, and I would like them to last another 20
years or so while enduring being turned off and on once or twice a
day. Will the step-start process ensure that kind of longevity?
Leaving the amp running 24x7 isn't an option due to fan noise and
power consumption.

Bill W5WVO