In the circuit shown, $I_1=80$ mA and $I_2=4$ mA. Transistors $T_1$ and $T_2$ are identical. Assume that the thermal voltage $V_T$ is $26$ mV at $27^{\circ}C$. At $50^{\circ}C$, the value of the voltage $V_{12}=V_1 - V_2$ (in mV) is _______.