If $\overrightarrow \alpha $ = $\left( {\lambda - 2} \right)\overrightarrow a + \overrightarrow b $  and  $\overrightarrow \beta = \left( {4\lambda - 2} \right)\overrightarrow a + 3\overrightarrow b $ be two given vectors $\overrightarrow a $ and $\overrightarrow b $ are non-collinear. The value of $\lambda $ for which vectors $\overrightarrow \alpha $ and $\overrightarrow \beta $ are collinear, is -