Tube DIY Asylum

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RE: Operating 71A above published max plate voltage

Posted by Paul Joppa on July 22, 2017 at 21:45:58:
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!