It is not simply a swap of transistors for vacuum
tubes, they are
fundamentally different approaches to gate design, at least if we're
talking about the common families of RTL ICs (that I've seen internal
schematics for).
Well, for one thing, isn't RTL generally bipolar junction transistors?
Vacuum tubes are operationally more like FETs than they are like BJTs.
(A BJT is current control, current output, whereas a FET or vacuum tube
is voltage control, current output.)
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