On 7/21/20 11:23 AM, dj7ww@t-online.de wrote:
Before WX0B switched to use feed through insulators I replaced two of his
baluns on Optibeams at a friend.
Baluns were made from RG393 wound through ferrite toroids.
Around the stainless steel screws the boxes were burnt out, I guess that was
caused by current, not by voltage and went into a loose connection and
thermal runaway.
Did the nut on the screw come loose or similar? I can see a temperature
cycling slowly loosening it, and then once it starts to get loose, the
temperature cycling could get a lot worse.
The "classic" way to avoid this would be to make sure there's enough
torque that there's always sufficient preload. I'm not sure what that
would be. For 1/4-20, it would be pretty high compared to #6 or #10
machine screws. I'm thinking single digit ft-lbs, which means with a 6"
long wrench, you're pushing pretty hard on it.
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