[AMRadio] Free Mercury

D. Chester k4kyv at charter.net
Sun Apr 27 12:39:25 EDT 2008

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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