HHO generator can be used for soldering brass instruments.The solder joints is the most common damage occur to a brass instrument during brass instrument repair work.

What is brass instruments solder?
Solder is used, just the same as with copper pipes used in plumbing. This is frequently referred to by musicians and repair clients as "welding" but in fact it is not welding. Welding involves extremely high temperatures and actually fuses two pieces of metal together into one piece of metal. The solder most common on brass instruments is "soft solder" which melts at relatively low temperature (around 350°F) and serves as a sort of "glue" holding two different pieces of metal together. This is usually a 70-30 or a 60-40 solder and uses a liquid flux.The other sort of soldering used on instruments is called "silver solder" and really is a sort of welding but is rarely referred to as welding. Silver solder is used to rebuild broken pieces, such as a broken brace which would then be soft soldered onto the instrument. Resin-core solder such as is used for electrical work should never be used as it won't hold properly. Only solid wire soft solder should be used, with a liquid flux.(this is from music instruments repair)