  We studied iron-based superconductors of various families with critical
temperatures covering almost all range $T_C = 9 - 53$ K. In natural arrays of
contacts formed in these materials we observed intrinsic multiple Andreev
reflections effect (IMARE). By using IMARE spectroscopy, we detected the
two-gap superconductivity, determined the value of the large and the small
superconducting gaps, and the corresponding BCS-ratios. The temperature
dependencies of the large and the small gaps $\Delta_{L,S}(T)$ are similar for
various families of the Fe-based superconductors and could be well-fitted in
the framework of the two-band model by Moskalenko and Suhl. We concluded on the
extended s-wave symmetry of the $\Delta_L$ order parameter (20-30 % anisotropy
in k-space) and on the absence of nodes for $\Delta_S$. The BCS-ratio
$2\Delta_L/k_BT_C \approx 5.2$ is nearly constant within the whole range of
$T_C$ (this means that coupling rate is unchanged), reflecting the 20 %
reduction of the $T_C^{local}$ in relation to the eigen $T_C^L$, and the large
gap roughly corresponds to the energy of magnetic resonance $2\Delta_L \approx
E_{res}$. This result requires a special theoretical consideration. Our
estimation of the relative coupling constants and eigen parameters of each
condensate (in a hypothetical case of a zero interband interaction)
$2\Delta_L/k_BT_C^L = 4.2 - 4.8$ and $2\Delta_S/k_BT_C^S = 3.5 - 4.5$ leads to
indirect conclusion that namely a strong electron-phonon interaction in each
condensate described in the framework of the Eliashberg theory plays the key
role in the superconductivity of iron-based oxypnictides. With it, the two
condensates interact weakly with each other. The observed scaling of
$\Delta_{L,S}$ with $T_C$, as was discussed above, is caused mainly by changing
of the density of states $N_{L,S}$ in the bands, whereas Ln-O spacers act as
charge reservoirs.
