Arced bandswitch removed from an Ameritron AL-82 (2, 3-500Zs)
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 V-withstanding ability on the undamaged part of this bandswitch tested at a bit over 5000 volts (120m. altitude). There is no obvious reason why this bandswitch should have arced in an AL-82.