. Electronic apparatus for biological research. Electronic apparatus and appliances; Biology -- Research. HEATER POWER SUPPLIES A better method is to use a 'hum-dinger.' This is a low resistance poten- tiometer—some 50 ohms—connected as in Figure The shder is then adjusted until the 'hum' is minimized. The effect of inductive coupling is reduced by tightly twisting the heater wiring, so that the magnetic fields due to the two wires as nearly as possible cancel {Figure ) and by the A^/ A^/ ''^«^' 3 50fl Figure X /. Figure use of valves having heaters of special construct
. Electronic apparatus for biological research. Electronic apparatus and appliances; Biology -- Research. HEATER POWER SUPPLIES A better method is to use a 'hum-dinger.' This is a low resistance poten- tiometer—some 50 ohms—connected as in Figure The shder is then adjusted until the 'hum' is minimized. The effect of inductive coupling is reduced by tightly twisting the heater wiring, so that the magnetic fields due to the two wires as nearly as possible cancel {Figure ) and by the A^/ A^/ ''^«^' 3 50fl Figure X /. Figure use of valves having heaters of special construction aimed at minimizing magnetic field production, such as the Mullard EF86, Osram Z729, etc. In the highest class of amplifier it may be safer to excite the heaters of low-level stages from direct current, and if the apparatus is direct coupled, a stabilized heater supply may be advisable as well. The simplest heater supply which also is fairly stable is the lead-acid accumulator, but the cells should be large— a 6 V car battery—so that the method is bulky and, in so far as accumulators need careful maintenance, not very con- venient. It is possible to make heater supplies by transformation, + o- dc. out — o- J. '"^ pF 1H. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Donaldson, Peter Eden Kirwan. New York, Academic Press
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