If the MV rectifiers have been sitting around a long time, especially if
they have been stored in anything but a vertical position, I let the
filament run at least 24 hours before applying power. If there is visible
mercury on the glass I would cook them until it disappears. If the arcing
did not leave any visible deposit on the glass or crud inside the envelope,
you can probably still cook them and they will eventually work OK.
I have heard suggestions to start them up for the first time using a variac
on the plate transformer, and slowly increase voltage. If they arc over,
back off on the voltage and let them cook for a while longer, and try again,
until you can reach full voltage without an arc.
If there is visible black crud inside, that looks like the ashes of burnt
newspaper, the tube is probably NG. That stuff tends to peel off the anode
of tubes with many hours on them, and the tubes nearly always arc over no
matter what.
Don k4kyv
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