If you got some fire brick and two torches you should beable to get the tube up to temp well enough.
The thing is for brazing to work the gap can not be too small or too big for the capillary action to work well. A small crack may be problematic for the filler to be suck in. The gap will reduce with heating too this may make things more difficult. Try asking on the frameforum or the frame builing section of bike forums. They will know the finner details of this.
There other rod may do the job though. HTS 528
If you got some fire brick and two torches you should beable to get the tube up to temp well enough.
The thing is for brazing to work the gap can not be too small or too big for the capillary action to work well. A small crack may be problematic for the filler to be suck in. The gap will reduce with heating too this may make things more difficult. Try asking on the frameforum or the frame builing section of bike forums. They will know the finner details of this.