Vacuum tubes don't have the longest "natural" lifespan, but you also have to remember that early manufacturing techniques mean a lot more "bad batch" variability.
When part performance is more unpredictable, ease of maintenance is a much bigger deal for everybody all across the price/quality range.
What was the failure rate of those vacuum tubes, that they had to be so quick & easy to replace?
I'm also curious, if the cathode was grounded to the machine frame, how dangerous was it to do work on those machines?
Vacuum tubes don't have the longest "natural" lifespan, but you also have to remember that early manufacturing techniques mean a lot more "bad batch" variability.
When part performance is more unpredictable, ease of maintenance is a much bigger deal for everybody all across the price/quality range.
Author here. I've powered up another tube module from the IBM 604, so let me know if you have questions...