sofie wrote:
: No steel wool... You don't want that stuff around electronic components
: or circuit board.
: Usually the contact in those TO-3 sockets are real good.... just unplugging
: and then re-plugging in the transistor will be all that is needed. For
: clean up use contact cleaner or in the worst case a pencil eraser to remove
: oxidation and then contact cleaner.
: My best advice.... if it's not broken, don't fix it. This would not be
: the cause of humming.

Agreed.

The TO-3 leads typically are plated or tinned. Using an abrasive on them
may reveal a more-readily oxidizable metal in the core of the transistor
lead.

b.