[Arran]

I wonder why the brown slide switches would be more fragile then the black ones? Are the slides made out of a different material, such as polystyrene verses black Bakelite?
  I've run into 7868 tubes before, in the power amp for a Rowe-Ami juke box. I think that they are another one of those tubes that the tube division of RCA developed, sort of a solution to a problem that nobody had. In any event I told my friend with the juke box that if those are shot then it would probably cheaper and easier to replace them with a pair of 6L6s by tossing out the magnoval sockets in favor of octals, or at least by making adapters.
Regards
Arran