Freiburg 7 -- FM Tuning rod question

      I am beginning my next project -- a Freiburg 7 Automatic. It has not been well treated. There is plenty of corrosion. In addition, someone in the distant past tried to correct some automatic tuning problems. The motor was nearly siezed.



      I feel, however, I can correct those problems. My question concerns the glass FM tuning rod with the silver slugs. I read with interest in Achim's project his incredible effort to restore his Freiburg. Did he have those slugs re-plated or did he just clean them?



      Mine are rather badly tarnished. Can I just remove the tarnish? Or does it need to be re-plated? Regards, Jim

      Hi Jiim,

      as for the FM slugs my advice would be to wait till the end. If everything else is working o.k. you should test the quality of the FM reception after carefully cleaning the slugs.

      If everything's o.k you're fine, if there occur problems with stations at the upper end of the dial at around 104 or 108 additional effort is needed.
      Same goes for poor FM reception at all frequencies.

      I cleaned the slugs very careflully until they became shiny again. After that the remaining silver coating had vanished. So I had them copper plated, then silver plated (25 micrometers) and finished with a very thin gold layer (0,4 micrometers).
      However, the gold layer mustn't become too thick since this decreases the slug's performance at high frequencies.
      The gold just has to prevent the silver from rotting, it has no electrical purpose. You will also get along without the gold layer but some protection for the silver seems reasonable.

      This is considered to be the best practise for solving this problem , but note that this issue is still undergoing heavy research here at the Saba board.
      Achim