The nonlinear self-consistent theory of two-stream superheterodyne free electron lasers (FEL) with pumping of retarded electromagnetic wave (Dopplertron-type) is developed. The main attention is devoted to the comparative analysis of single sectional and klystron-type schemes of Dopplertron and H-ubitron FELs. These systems are based on application of two-stream instability as a work effect simultaneously with three-waves parametric interaction mechanism which is traditional for FEL. One- and three- sectional of superheterodyne FELs (SFEL) are researched. The first section of klystron scheme plays grouping role, second one is transit space and the third plays demodulator role. It is found out that single sectional SFEL and three- sectional SFEL klystron-type have approximately same gain factors. Therefore a klystron-SFEL is a very promising design because of them great simplicity. In this connection it is shown possibility of creation of FEL-amplifiers which have approximately 30-40 dB amplification levels in mm-IR ranges.