What type of gas torch should i use to braze 1" OD 3mm walled aluminium tubing?

A lot depends on how big the item is. aluminum is great for carrying heat away. so if it's a small piece, a propane torch is capable of heating it. but if it's a substantial piece, you will need to get more serious. oxy acetylene is the most serious heat producer, but is rather expensive to set up. It gets plenty hot to melt right through the aluminum so be careful.