Well there is a guy (Velonomad) who's quite build a few frame with your hardware store air-Mapp torch. So yes! The BB and crown will be difficult though, I think he used a piece of steel to reflect the heat. I actually fillet brazed 7/8x0.049 tubes w/ brass on a air-Mapp. I brazed on top of a thick piece of angle iron as a "hearth".

So yes O/A is very hot as you waste the heat away most of the time, and it's easy to char/distort your work. But without it you have to resort to tricks that will make your life harder, and you risk of heating the work for a longer time and on a greater area.

Also w/ air-A or mapp you'll be limited to silver basically unless you have a hearth.

Another option is oxy-propane. It's the set-up I'm building up.