Brazing must achieve penetration in the overlapped joint area. To make this possible, both plates need to be the same temperature.

Cut the test piece to separate lengthwise as shown: Joint passes inspection if there is copper silicone filler wire transfer on the lower plate as shown below.

Without a pulsed MIG welder, it is difficult for the lower plate to reach the required temperature. If the bottom plate does not reach the correct temperature, brazing filler remains on surface, and you cannot achieve sufficient strength.