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EC's transistors are quite low-speed devices, with high internal capacitance. Here, they're used in common emitter mode, which is sometimes described as slow, to amplify a 100MHz signal. Each of the 2 amps has 14.4dB gain, together they have 28db gain.
Input impedance is 50Ω.
There is no negative feedback because transistor gain has little effect here, a 10:1 range of forward beta creating only 0.55db variation in gain. Perhaps the internal capacitances create some sort of negative feedback. If so, I wouldn't expect this to work correctly across a wide range of frequencies.
It probably is a matter of internal capacitance because replacing the output with a Darlington pair results in a severe loss of gain, actually attenuating at best.
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