[klondike98]

Thanks for the comments. Strange thing is, its not a hot chassis. The "ground" is not the chassis. The common lead for the electrolytics (B- ) is what all the "ground" connections are connected to except for the tube Pin#1 connections. Those Pin 1 connections do go to the chassis so the wiring is not quite what the schematic reads.

The screw is the "external antenna" connection.

The set screw is an 8-32 so my first approach will be to put a slightly longer 8-32 set screw in place and see if there are enough threads still holding to make the knob work. Second approach will be to fill the thread hole with epoxy putty and drill/tap an 8-32 thread. If that fails I'll drill/tap a 10-32 thread.