alt Hacker NewsWhat 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?
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Over on Youtube the Usagi Electric channel has several videos about reviving old vacuum tube computers and one of the interesting aspects is that tube failures are much less of an issue than the germanium diodes. The tubes are large and dramatic, but they're heavily outnumbered by the diodes. It was such a problem that the company built specialized test equipment that could identify bad diodes on the cards.
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.
> I'm also curious, if the cathode was grounded to the machine frame, how dangerous was it to do work on those machines?
When ground means earth, then: The chassis isn't dangerous at all. Its potential relative to other nearby things that are also connected to earth is ~0v.
When that's used as a supply rail (like for the cathode), it still works fine. It's still tied to earth.
You don't want to put any of your dinguses betwixt that and the +150v plate rail, but... I mean. :)