When carrying out welded repairs to frames, make sure the welded joins are clear of any brazed lugs. The inclusion of any brass from the brazing will render the welded joints brittle (with the risk of subsequent failure). When I had no option but to make a welded repair close to a lug, I cut the lug back, welded the 2 ends of tube back together, then built up the lug again with silicon bronze rod (making the repair invisible). This is the method I have adopted for repairs to the rear of the lower frame tubes on Mark series machines (where you dont have the luxury of being able to fit an internal sleeve due to the presence of the torsion bar).
Regards,
Eddie.