Hi Ray,
Breaks at the top of the front down tube usually occur about 1" or so from the lug - this is where the reinforcing inner sleeve ends. For some strange reason, Mr Douglas decided to make these sleeves with a blank end - thus concentrating the stresses at that point. When I have built/rebuilt frames, I have remade the sleeves to be open ended and have tapered the bore at the lower end to help spread the stresses. I have never had a frame fracture again (or even crack the paint) in that area.
Re-tubing in this area is not easy as the down tubes are quite deeply socketed into the head lug. Also, if you have a bronze head lug, you will probably have to get the old tubes machined out as heating to un-braze them will result in the lug being at the point of collapse when trying to withdraw the tube. If it was my frame, I would be inclined to check out the area of the break and make sure there is no sign of braze within ½" or so (the braze seldom penetrates that far down between the tube and the inner sleeve), then 'V' out the joint and get a trusted welder to TIG weld it back together, but be sure to prevent any brass inclusion in the weld as this will seriously compromise the strength of the joint. Properly TIG welded, the joint should be almost as strong as the parent tube and any heat damage will be confined to the area of the repair.
Good luck,
Regards,
Eddie.
