Of course, you couldn't use water if the cap had DC on it. Eventually, it would
leach something out of the cap that would cause some conduction, and then you
would get electrolysis.
The problem with vacuum is keeping it that way, Hi!
I never tried sending an apprentice to stores for a new vacuum for a variable
capacitor.....I did catch one out by suggesting that turning an SSB filter round
on the PC board would produce the other sideband!
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