When you are connected to buffer a tester to outside tool, we should have an booster with enough bandwidth and power disposition ability. This circuit is a very simple for unity gain buffer; it is only two pairs of emitter followers. The base emitter voltages of Q1 and Q2 cancel out, and so do those of Q3 and Q4. The preset is used to zero out any small dc offsets due to mismatching in the transistors.
It has reasonably high input impedance, 50 ohm output impedance, a wide bandwidth and high slew rate.