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Published online by Cambridge University Press: 24 October 2008
The characteristic relationship subsisting between anode current ia, anode potential ea, and grid potential eg in a well-evacuated thermionic triode, viz.
leads to very simple analysis of the circuit conditions when μ, is a constant and φ is a linear function. In all the usual applications of triodes, μ is very nearly a constant; in some applications, e.g. in good acoustic amplifiers, over the working range φ is very nearly linear; in others, e.g. in rectifiers, non-linearity is essential to the performance. In oscillators, and in power amplifiers used with them, both conditions are met. Where a sinoidal oscillation is desired, i.e. an alternating current as devoid of harmonics of the fundamental frequency as can be contrived, the working range must be sensibly linear. A feature of such a régime is that the major portion of the power supplied to the triode must be dissipated in heating the anode. Where higher efficiency is required, the cycle must be made to extend beyond the linear range, and harmonics are necessarily introduced.
* Thus in a small receiving triode, Osram “ DEH 410,” measurements at ia = 4000, 2000, 300, and 50 μA. showed values of μ respectively 36·5,38, 36·5, and 34.
† A useful term introduced by W. H. Eccles.
* It has been suggested (Martyn, D. F.—“Frequency Variations of the Triode Oscillator,” Phil. Mag. Vol. 4 (1927), p. 932CrossRefGoogle Scholar) that it is impossible for a self-oscillator to limit its amplitude to a cycle in which the grid never becomes positive. That this is a mistake will be obvious from the analysis, and is easily demonstrated by direct experiment with a suitable triode.
* The sense of M is such that, if the two coils are coaxial, they are wound in opposite ways.
* There is no obstacle to making ωL < < ρ although, as will be seen below, it is desirable that 
shall have a value upwards of 2p. A low power-factor f is provided in order to give stability of frequency, and to keep harmonics in the oscillatory circuit much weaker than harmonics in the anode current.
* Instead of the 50% often mistakenly stated.
† Taken with anode potential constant at 200 V.
‡ The value of p given above (11·4 kΩ) is actually the sum of the measured anode resistance (11·2 kΩ) and this inserted resistance r.
* Witness the use of the high-power triode “LS 5” with 300 V for outputs of the order of 2 V.
* In the practical use of a triode oscillator, R r would ordinarily be adjusted by the “anode tap ” method, i.e. by choice of the point along L at which the anode is connected into the circuit. This would have been less convenient for the present study, since it would have complicated the exact analysis and prevented the determination of Rr from the simple formula 
† This measurement of I a was made by a triode voltmeter connected across a suitable known resistance placed in the anode circuit. Because of the effect which this rather large added resistance would have upon the performance of the oscillator, 
was measured in this manner only during the preliminary check of the values of R r.
* The cyclic values under these conditions are plotted to scale in Fig. 7.