  Using the self-flux technique we grew superconducting
$(K_{1-z}Na_z)_{x}Fe_{2-y}Se_2$ (z = 0.3) single crystals. The EDX mapping
revealed the uniform elements distribution on the crystal surface while the XRD
measurements indicate that the crystals are compositionally inhomogenous on
nanoscale. The physical properties of the as-prepared sample are characterized
by electrical resistivity, magnetization and specific heat measurements.
Resistivity measurements show the onset of the superconducting transition at 33
K and zero resistivity at 31.7 K. The large upper critical field $H_{c2}$(0)
was estimated as high as about of 140 T for the in-plane field and 38 T for the
out-of-plane field. The anisotropy of $H_{c2}^{ab}(0)/H_{c2}^{c}(0)$ and
coherence lengths $\xi^{ab}(0)/\xi^{c}$(0) was found to be around 3.7. The
pioneer studies by multiple Andreev reflections effect spectroscopy
("break-junction" technique) revealed the presence of two anisotropic
superconducting gaps $\Delta_L\,=\,(9.3\pm1.5)\,meV$,
$\Delta_S\,=\,(1.9\pm0.4)\,meV$, and provided measuring of the $\Delta_L$(T)
temperature dependence. The BCS-ratio for the large gap
$2\Delta_L/k_BT_c^{bulk}\,\approx\,6.3$ points to a strong electron-boson
coupling in the "driving" condensate characterized by $\Delta_L$ order
parameter.
