Zinc will vaporize out of the brass in the hydrogen/nitrogen atmosphere. If Cu-Sn bronze is used there will be no Zn vaporization problem.
When using brass, plate with 0.0005 in of electrolytic nickel to prevent Zn vaporization and improve brazability. For best brazability it would be best to plate the Te-Cu with 0.0005 in of electrolytic nickel also to assure good wetting of the Te.
In place of plating a dilute white silver brazing flux may provide adequate wetting.
Suggest using a brazing filer metal of AWS BAg-8 (Ag-28Cu) at 1475°F or AWS BAg-18 (Ag-Cu-Sn) at 1400°F
The dew point of the atmosphere is important when asking such questions and it was not included. Ni Plating will allow good brazing at the higher dew point atmospheres, 30-80°F dew point. Bob Peaslee