I need to remove an aluminum knob from a radio, but the Allen setscrew
is stuck solid.

I've tried:

-- WD-40
-- Kroil
-- an Allen wrench with a long handle (bent handle)
-- an Allen 1/4" drive socket (twisted the Allen part)
-- blocking up the knob with rubber blocks and beating on the Allen
wrench while turning
-- heating the Allen wrench with a heatgun while engaged with the
setscrew and turning
-- heating the Allen wrench to 450 degrees and then inserting it into
the setscrew and turning

All this and the bloody thing is still stuck solid. As a last resort
I know I can drip 1-mole nitric acid into the hole, which would eat
the steel setscrew and leave the aluminum relatively untouched. This
I have done on aluminum car engines with snapped-off manifold bolts
and it works great.

However, I can think of a bunch of ways this could go wrong when
applied to a rare radio.

I would greatly appreciate any ideas.

Thank you.

73,
Jeff
N6MNI