Scrap frames can be cut up and used to hone your brazing skills for nothing other than the cost of cleaning time and filler rods. You can also buy straight 4130 and make your own pseudo-lugs using two close sizes that slip over each other. Cee-way sells cheap lugs for learning too, but you can make do with junk frames.
Cut apart your joints and see how well you the brass into the joints. I used to braze copper heat-exchanges for a living and have heaps of time on the torches... I'm learning smaw welding for work now... MIG and TIG tickets will follow in time.