In the debate between tubes and solid state, it is interesting to look at the technical commonalities and differences in the two technologies.
The following is a quote from “Thermionic Emission”, by Wayne B. Nottingham, “Technical Report 321”, December 10, 1956. What is interesting is the proportionality equation number 82.1:
The exponent is believed to be negative in this expression because VT is negative.
The semiconductor conducts according to this approximation (from A.S. Sedra and K.C. Smith (2004) Microelectronic Circuits( 5th ed). New York: Oxford. Eqs. 4.103–4.110, p. 305 ISBN 0-19-514251-9):
Do see any difference between these functions? Both are proportional to e to a power, varying according to input voltage. I0 for the vacuum tube and Is for the bipolar transistors are simply scaling factors. Both operate on the same exponential curves.
Based upon this, it is fair to say that there is no difference between a bipolar transistor and a triode, when operating in the linear parts of their active regions. In other words, both amplify the same in the “clean mode”.