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[uvcm inc.]

Mercury ref tubes of all types have mercury that sticks to the glass and
components inside.
Depending on the brand, type and year made the mercury deposits very a great
deal.
This is not a bad thing. If the tube has not been used for a while or has
been stored on its side, it is best to COOK THEM FOR A FEW HOURS BEFORE
APPLYING PLATE VOLTAGE.
The 3B28 is a newer style and a better ref tube; it also has mercury in it
but less.
If you need any more info be glad to help. 
I have several patents in mercury vapor designs
Brad KB7FQR



those flakes in your 866s are mecury.  if they haven't been run in a  while 
you should let them sit with just the filaments on for a while, to make
sure 
the stuff gets where it needs to be. They look nice, but the mercury  vapor 
rectifiers need to be treated well especially after a long idle  period.
You 
can direct sub a 3B28 argon rectifier tube, and not  have to worry about the

866s. They don't glow as much, but are more tolerant  tubes.
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