So books on VT electronics are quite hard to come by these days and many electronics textbooks don't mention thermionic valves whatsoever. I managed to find a very good vintage book : Vacuum tube and semiconductor electronics(Millman, 1958).(adsbygoogle = window.adsbygoogle || []).push({});

It describes the triode plate current characteristic curve as defined by the equation:

[TEX] I_{A} = g_{m} = \sqrt{V_{G} + \frac {V_{A}{\mu}^{3} [/TEX]

Where μ is theamplification factorand g_{m}is thetransconductance.

But another book defines I_{A}= f(V_{A},V_{G}) and expands it into a taylor series. Now first question is: Are the amplification factor and transconductance constant characteristics of the tube and if not, what are the independent variables which they depend on and how can they be calculated?

Also, is the first equation an aproximation? Because in another book it shows the triode current curves plotted against anode voltage for both negative grid voltages and one for positive grid voltage and when the grid is positive the curve has an inverted parabolic shape whereas when V_{G}< 0 the curves arealmostlinear.

So in a nutshell, what's thebestfitmathematical model of the triode anode current if you know the grid voltage function V_{G}(t) and the voltage applied to the anode?

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# The triode current equation

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