I tried few months ago welding (not brazing) with tig and mig on unknown types of brass and different thicknesses (around 1/16 to 1/2, 1-12 mm). 2 types of fillers with tig ja CuSi3 with mig. The main takeaway for me was the reason why preheat is recommended for brass over 1/4 thickness (when arc welding).
Tried hot start on mig (synergic for wire and its thickness, in this case 0.030, 0.8mm) and zinc immediately just poofed out. Automatic settings with thickness (for fillets) were no match. On steel worked fine, on stainless with little adjustment and on brass not at all at least without preheat.
So, week or so after that I tried tig. Whether or not had a gas lens and 5,6,7 size cup didn´t matter after poofing out. I slowly realized what was happening. I had recently done oxy-acetylene brazing with brass filler on 1/8 and 3/16 (3 to 6mm) with other part being different and same thickness. Filler does poof out if you heat it directly (and so does flux if over heated, temper colors!).
Tried pulse on tig. First peak being lot higher (120-160 kinda like micro tacking) compared to background current and it worked on some (later realized that these were with low zinc content plates for decoration and as that quite versatile stuff). On others zinc poofed out from the get go. So tried around 55 to 65 A without pulse using torch trigger (pedals are rare around here). After waiting it to puddle ever so slightly and then adding filler it worked out great. Also tried backing up to puddle and keeping arc on puddle which also worked. Mix tig (10% on AC) seems to have applications like Johannes Ciobanica said in podcast. These applications and their correct use on different materials are yet up for testing to me.
But one of filler wire types had wrong paper tag on it and I am pretty sure it contained aluminum, which I concluded from the film on surface. Looks funky when see no puddle and adding filler makes surface come up. Not a good sign in any case. AC worked with that filler. That filler also balled up like aluminum wire when your work angle is out of balance and it gets "preheated".
I had respirator (P3 class) and fume extractor plus didn´t keep head over the gasses. Trials took hours. Never have had (serious) zinc fever nor do I want to.