. Electronic apparatus for biological research . Figure input type. On light load this arrangement gives an output voltage of approximately {Ifl^ X 200 = 283. A little thought reveals that the peak inverse voltage across the rectifier occurs in the middle of the non-conducting part of the cycle and is 566 V. Sometimes it is explicitly stated that the V. of a rectifier is, say, 600 V, rendering it suitable for this application, but it may also be described as a '200 V rectifier, referring to the maximum trans- former voltage. In looking at manufacturers' Hterature it is necessa
. Electronic apparatus for biological research . Figure input type. On light load this arrangement gives an output voltage of approximately {Ifl^ X 200 = 283. A little thought reveals that the peak inverse voltage across the rectifier occurs in the middle of the non-conducting part of the cycle and is 566 V. Sometimes it is explicitly stated that the V. of a rectifier is, say, 600 V, rendering it suitable for this application, but it may also be described as a '200 V rectifier, referring to the maximum trans- former voltage. In looking at manufacturers' Hterature it is necessary to be very careful which figure is being quoted. POWER RECTIFIERS These fall into three groups: (1) Types for supplying HT to valves, a few hundreds of volts at a few tens of milliamps. (2) Types for supplying 'extra HT' to cathode ray tubes, image-converter tubes, photomultiplier photocells and the like. These deliver a few thousands volts at a few milliamps. (3) LT types, for making a few volts at a few amps. Important uses for these are accumulator charging, and the generation of direct heater current from the mains. HT rectifiers Some HT rectifiers are shown in Plate Nos. 1, 2 and 3 are selenium- iron and are rated at 120, 60 and 30 mA '125 V', the is about 350 V. Notice the cooling fins; these components should be mounted in the attitude shown so that optimum convection occurs. The forward resistance of these units is such that about ^ of the no-load output voltage is lost on full load. Nos. 4 and 5 are copper-copper oxide and are contact-cooled, that is, they are bolted against the chassis and the heat generated is removed by conduction. They are rated at 120 and 60 mA respectively, 125 V, so they correspond to the selenium iron units above them. No, 6 is a germanium junction type. Provided it is kept properly cool (<25°C) by suitable siting in the apparatus and by bolting it firmly down to a metal sheet, so that the heat generated is conducted aw
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