[Heathkit] Help with removing of knobs.

[OTAKEBI at aol.com]

I have two knobs on an SB-100 which have had the Allen screws stripped  and 
can't be removed.
The Allen Key just turns in the screw.
I have gone to the next size up but no go.
Before I start to invent ways of removing these things can I get any  ideas?
I do not want to destroy the knobs since I am in need of them for a  
restoration project.
I have more screws so those can go since they are stripped anyway.
Thank in advance,
Dan/N4VET