On Nov 26, 8:41 pm, (Dave Platt) wrote:
Unfortunately, the homebrew cap you're looking at uses threaded brass
rods, brass nuts, and aluminum plates. None of the connections are
soldered. The connections to the stator plates will be
interference/friction mating (i.e. brass nut, tightened onto aluminum
plate) and I'd be concerned that the aluminum will soon oxidize and
that the connections may rise in resistance, leading to increased
losses over time.

This issue could be largely eliminated if you were to use sheet brass,
rather than sheet aluminum, for the stator plates. You could then
flux and solder the rods, nuts, and plates together (before installing
the acrylic endplates, of course :-) and ensure a solid, reliable,
low-resistance current path.

In the real world, most non-miniature variable capacitors were made
with spacers and plates that weren't soldered all together, and
generally didn't use star washers or anything except at the connecting
posts. But these are generally either all-brass, all-aluminum, all-
steel, etc., and not a mismash of different materials. You don't
explicitly say so, Dave, but are you implying that it's the dissimilar
materials that are the problem, or that it's the use of aluminum? My
personal taste would be to make it out of all-brass.

After the 50's, for the miniature variable capacitors, they seem to be
made out of material that has been silver-soldered together without
any explicit spacer components. (Maybe brazed or spot-welded, in some
cases.) This seems to be either an improvement made for VHF/UHF work
(remember when 50MHz was UHF?) or an admission that using spacers
doesn't make economic sense when components are so tiny.

Tim.