. Electronic apparatus for biological research . EHT- (a) (b) RFEHT Figure In this method power is drawn from a HT supply to feed a radio-frequency LC oscillator. The oscillator inductance forms the primary of a step-up transformer, whose secondary voltage is rectffied and smoothed to form the EHT. Because the frequency is high the necessary high voltage smoothing and input capacitors can be quite small, of a capacity insufficient to hold a lethal charge. The step-up transformer is a simple air-cored affair, and the overall cost, despite the extra valve and associated small components, i
. Electronic apparatus for biological research . EHT- (a) (b) RFEHT Figure In this method power is drawn from a HT supply to feed a radio-frequency LC oscillator. The oscillator inductance forms the primary of a step-up transformer, whose secondary voltage is rectffied and smoothed to form the EHT. Because the frequency is high the necessary high voltage smoothing and input capacitors can be quite small, of a capacity insufficient to hold a lethal charge. The step-up transformer is a simple air-cored affair, and the overall cost, despite the extra valve and associated small components, is probably no greater than that incurred in generating EHT from 50 cycles. An RF supply giving —2,000 V at 1 mA has been described, including details for making the RF transformer, by Dickinson^^ and has the circuit of Figure Notice that the EHT rectifier circuit is of the type d in Figure This throws more strain than is absolutely necessary on the trans- former insulation, but allows Dickinson to heat his rectifier valve from the common heater supply. 598
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