. Electronic apparatus for biological research . —r-—EHTf Astigmatism Figure without serious distortion. Such a circuit is not therefore of much use in electrophysiological work, but it illustrates the kind of network to be found in certain commercial oscilloscopes. Notice how the shift potentials are applied in push-pull; the sliders move up or down each ganged potentio- meter together. Notice also the astigmatism potentiometer for finding the optimum focusing conditions. The cathode ray tube heater is fed from a special winding on the mains transformer, insulated to withstand the EHT v
. Electronic apparatus for biological research . —r-—EHTf Astigmatism Figure without serious distortion. Such a circuit is not therefore of much use in electrophysiological work, but it illustrates the kind of network to be found in certain commercial oscilloscopes. Notice how the shift potentials are applied in push-pull; the sliders move up or down each ganged potentio- meter together. Notice also the astigmatism potentiometer for finding the optimum focusing conditions. The cathode ray tube heater is fed from a special winding on the mains transformer, insulated to withstand the EHT voltage. The capacitor across the 'brightness' variable resistor is important; the degree of smoothing provided on most EHT power supplies is sufficient to steady the inter-anode potentials, but the spot brightness is extremely sensitive to variations in grid-cathode potential, and additional smoothing is invariably required here. About 0-5 ^F is generally sufficient. The calculation of the values required in the resistor chain is quite easy. 457
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