If the amplification and shaping circuit of pulse signal is composed of triodes, the emitter configuration circuit is generally adopted, that is, the emitter is directly grounded or connected to the power supply terminal), the base input and the collector output;

In this * * * injection circuit, the output and input of each stage are in opposite phases. According to your question, you need a two-stage injection circuit, that is, you need to reverse the phase twice to get the signal in phase with the input terminal;

To construct a two-stage emitter circuit, two PNP transistors or two NPN transistors, or a mixture of PNP and NPN, can be used.

If only one triode is used, in order to get in-phase output, it can only be connected in the form of * * * collector, that is, emitter output mode. As shown in the figure, the signal is output from pin 6 of 6N 137. Because the other end of R3 is connected to the power supply terminal, it must be a PNP tube here, so the output high level can be =50V, but the output low level will be higher than 0.7V: if an NPN tube is used, the other end of R3 should be grounded.