I love this discussion on materials used to join bike tubes. As a demented teenager, instead of playing baseball, I hung around Drysdale's shop on Canal Street in New York City. He would put the assembled and pinned frame on a bed of coals (I think he used gas) and heat the entire frame before he would begin brazing the lugs. I have no knowledge about frame building, but Drysdale's technique would seem to limit heat stress, where part of the tube is very hot and cool elsewhere. Also, judging from my experience in making silver jewelry, the "all over" heat would promote quicker brazing with less material.
still demented in New York, NY