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In Reply to: RE: Operating 71A above published max plate voltage posted by Donald North on July 22, 2017 at 11:01:08
If NOS, it's a very old tube which suggests the vacuum is not as hard as more modern tubes. I would guess that's the limiting factor for that voltage rating - ions will crash into the cathode and "poison" it. More voltage means more velocity per ion.
That thought may or may not be the real thing, but you can be pretty sure there was a reason for the specification. We may not know for sure what that reason was, but it existed!
You raise a good point. However if operating the tube above max specified voltage can damage it, then why do they show plate curves at over twice this voltage? Wouldn't the tube have been damaged during the curve tracing process?
The manufacturer must take into account the possible voltage peaks with signal present. Extending the static curves doesn't damage the tube under test; it simply simulates the dynamic response when it's operated with the maximum recommended DC voltage.
Buy Chinese. Bury freedom.
Along with what Phil said, yes, so they damaged a tube or two to draw a complete set of curves. That was/is part of the expense of manufacturing electronic devices!
That is the quiescent voltage. Note on the curves -40 volts gives ~20 ma which is shown in the same column. With a signal present the plate voltage will swing considerably higher.
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