Glad to see that there is still intrest in this thread!!
When I build a double I use different solders for differnt parts. For the quater rib I use silver braze which flows at around 1500 degrees if I remember right. For the wedges I use a lead based solder around 50-50 which flows at around 150 degrees higher then Brownells 44 silver bearing solder which is what I use for the ribs.
If you solder the ribs with the 44 and use an welding torch I have found that if you crank the O2 up high you can put enough heat into the rib and barrel to get a good joint but not mealt the higher temp lead alloy solder. I chase my rib joints with a soaking wet paper towel and once you get it down you will not get a "cold joint".
By using several different tempriture solders you have a bit of lee way as far as softening up the other joints. It takes a bit of time to get the feel for this but for me it works great.