Where on the instrument is the hole? Could you patch it from the inside
with
brass or copper shim? You will need to get a dremel or similar in to
clean
up the surrounding area if you go down this route to get the solder to
take
but it might be possible, I've seen this method used to repair valve
ports,
apart from the cleaning the difficult part is holding the shim patch in
place while you solder it, this usually involves making up some sort of
'hairgrip' spring to hold it in place. K&S material centres (hobby
stores)
do a small pack of various thicknesses of shim.

Don Valentine

Don,
I think most repairmen would hang me if I put patches inside the tube.
There is too much of a chance of that throwing something off and giving the
horn a bad or even missing note.

LB