Right jig is best way there. So it time for some extra join practice. I like to use real tubing as the thickness effect how fast you have to work and how much you have to back the tourch off. Two mains styles i am working.

1. Traditional Big filet.
So basically it's a traditional capillary braze at first. I use a SIF 101 rod, with a neutral flame. Get the whole area up to tem and introduct the brazing rod, makeing sure it flows all the way around the join and is draw inside. Back the flame off a let coll a little until its all solid. This is important as the brazing material is harder to melt second time rount and that helps in thenext step. The is time to do a fillet braze ontop of that joint. this requires better heat control so i go slowly with a small nozzle. genlty working around the joint trying to make a nice even shap all aroudn the join with out sagging but also as smooth as you can make it.

2. Small fillet

With modern tubes that are really thin and new brazing rods small fillets have become more popular. I have be trying SIF no.2 rods with 5% Ni which are pretty much the strongest you can get. These only require a fillet that is just under 4 times the tube thickness. So a Nivachrome tube that is 0.8mm wide only requires a fillet of 3-3.5mm. The real trick is to try and do this in one pass to reduce heating time. Although the Nivachrome tubing is pretty tough in comparison to say a 753 tube.

See pics below:
Left joint is the big fillets (SIF 101 rod)
Right hand is the small (SIF2 C5 rod)