Key result
An experimental comparison of valve types for electromyograph amplifiers demonstrated that noise depends on grid bias and anode current, with a selected pair showing unprecedented low noise levels.
The study identifies optimal operating conditions and specific valve types to minimize noise in low-frequency amplifiers for electromyography.
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May guide valve selection to minimize noise in experimental EMG amplifiers; leaves open translation to clinical use or modern devices.
An analysis of the required sensitivity of electromyograph amplifiers is given in terms of the source impedance. Possible sources of noise in low-frequency amplifiers are discussed and estimates of their magnitudes made on the basis of previous published figures. An account is given of an experimental comparison between valve types, and an investigation of the effect of operating conditions; the noise depends on both the grid bias and the anode current. Spectral analyses are given of the noise from selected valves in the range 2 to 16 000 c/s. Persistent selection and good fortune have brought to light a pair of valves with a noise level lower than any previously reported in this frequency range (as far as the author is aware). Finally it is shown how, under certain conditions, the noise performance can be improved by means of an input transformer.
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A. Nightingale (1958) studied this question. Low-frequency valve amplifiers was evaluated. An experimental comparison of valve types for electromyograph amplifiers demonstrated that noise depends on grid bias and anode current, with a selected pair showing unprecedented low noise levels.
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