Arced bandswitch removed from an Ameritron AL-82 (2, 3-500Zs)

Even though the contacts are still intact, this bandswitch is kaput because the ceramic insulation is coated with condensed metal from metal vapour in the arc: (Courtesy of an amplifier repairman who wishes to remain anonymous.)

The open-contact withstanding ability on the undamaged part of this bandswitch tested at a bit over 6000 volts (120m. altitude). There is no obvious reason why this bandswitch should have arced in an AL-82.