SB-230/ 8873 tube change

[Steve Harrison]

At 11:26 PM 1/30/99 -0500, Leisman wrote:
>Dear all:
>
>When I change the 8873 tube in my SB-230, I am assuming I will need to
>clean the existing beryllium block free from the heat conductive gel,
>re-apply the gel or cream as I replace the tube.  Anyone know where I
>get the gel/ cream?, and, has anyone had any experience changing the
>8873?  What did you use to clean the beryllium block and what
>precautions did you take.

It's just ordinary silicone power transistor grease; get a tube at your
local Radio Shack. As for cleaning off the old stuff, use isopropyl alcohol
(if available; leaves little or no residue) and paper towel, napkins, rags,
whatever. The beryllia block is completely non-toxic and inert unless you
file, grind or otherwise do something to cause dust particles; so don't
sand it!! Don't scrub it, merely wipe the old gunk off. It would be a good
idea to handle it as little as possible, naturally. If you're concerned,
use dishwashing or vinyl medical gloves from your local drug store. I would
deposit the dirty rags and gloves in a sealable plastic freezer bag before
disposal. There isn't supposed to be any hazard with handling solid
beryllia blocks like that; and many of us have handled ceramic tubes with
abandon, not realizing that the base ceramic sometimes is beryllium oxide
(not in between the screen ring and the base or anode cylinder, but the
"ceramic" wafer holding the base pins itself).

Now, DISPOSAL of a broken block would be a different story since it's much
easier for chips and small particles to break off the broken edges.

By the way, I've heard that the silicone heat-transfer grease is really
more akin to the stuff that you spread over your baby's bottom so long ago.
It's messy, but apparently non-toxic when used as intended (at least, I've
never seen any hazardous warning). Use alcohol to wash it out of your
hands. Then wash your hands thoroughly with soap and water and a disposable
towel.

>Any help would be appreciated.  Ican't believe I'm the only one to run
>into the problem.

Remember that hundreds of two-way-radio techs have changed 8560AS Eimac
conduction-cooled tubes in commercial shops, which are also attached to
beryllia insulator blocks. So while there is hazard, it's minimal unless
you grind, crush or sand the beryllia block.

73, Steve Ko0U/1

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