Abstract
The usual input circuit for a head amplifier associated with a pick-up tube of the C.P.S. Emitron type is effectively a capacitance shunted by a resistance, the former consisting of the output capacitance of the tube and the input capacitance of the amplifier. An improvement in signal/noise ratio for the higher video frequencies is shown to be obtainable by modifying the input circuit by connecting an inductance between the two capacitances, and suitably equalizing the modified frequency/amplitude response. A weighting function is suggested for assessing the visual effect of the two differing noise spectra. The increase in noise resulting from the application of aperture correction for the pick-up tube response is considered, and some of the noise problems associated with gamma correction are discussed.The latter half of the paper describes a method of equalizing the frequency/amplitude response of the modified input circuit and considers some of the practical problems involved in designing a low-noise head amplifier. The conclusion is reached that a worthwhile improvement in picture quality is obtained by modifying the input circuit, and this is particularly so when aperture correction is used.
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