Quote:
Originally Posted by Argus25
Quite right, I noted it was an amorphous solid in post 7.
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You did indeed - remiss of me not to have acknowledged that!
Quote:
Originally Posted by Argus25
Some valve specs include operating positions for the valves, presumably this is related to possible deformation of the metal parts of the valve with heating and nothing to do with the glass.
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I think that's right - even reversible sag of grid wires as things get hot and expand.
I have seen caveats against base-up operation of high-power valves like KT88 unless fan cooling is employed, because airflow is impeded more by a chassis above than a chassis below.
Regarding misalignment of electrode structure, I'd find it difficult to accept that this was by mechanical shock! My experience of a dropped valve is that bits break off the glass pinch due to jarring. I've never thrown one around to see if I can get the metal wires to bend. (Button-based valves are more robust, they're OK till the envelope breaks). So I reckon that misaligned valves left the factory like that - but presumably still met test specifications (which may have been relaxed enough to allow slightly misaligned valves to pass).