  In this paper it is considered a spectral density for a class of Jacobi
matrices with absolutely continuous spectrum that was examined first by
Moszynski. It is shown that the corresponding spectral density is equivalent to
the positive continuous function everywhere except the point $x=0$. In the
point $x=0$ the spectral density may be finite as well as essentially infinite
depending on the parameter. So in this class we discover an example of 2nd type
spectral phase transition.
