I did use soft lead solder for my first two 2" O.D. boilers and solid parafin wax to heat boilers
to raise steam for oscillating engines. All these boilers fell apart when boiler was about to run dry or totally dry.:hDe:
Read books by Tubal Cain on silver soldering and seek professional advice from air conditioning contractors,plus a good friend who has good working experience with gas welding from using steel rods,brass rods and silver solder rods. His advice was most beginners use gas torches with insufficient heating power.The torches powered by small camping gas canisters will not provide the heating power.Bought Mapp Gas torches that comes with two burners and even three burners and these torches gave me enough brazing power. For bigger jobs,I use two Mapp Gas Torches.
Next advice was pickle,sand and clean up joint surface and apply Easy Flow Silver Solder Flux
and slowly heat till paste dries up before applying full power to dull red heat which is just after the flux liquidifies. Do not overheat.Dip rod into flux and prehit before plunging into joint. Do ensure you put in sufficient solder and with sufficient heat,the solder will flow by itself. Do not overheat.
There will be failures but if one persist, good silver soldering will happen after a few goofs.Gus had too many goofs.
For beginners , please practice on copper to copper. Copper to brass or steel is another game.
Practice makes perfect.