. Electronic apparatus for biological research. Electronic apparatus and appliances; Biology -- Research. +60, lAOk 1 + 60 50k ^3Q <iM X" Mm EF37A. Output Figure are triode-connected and facilities are provided for gain balancing. The time constant of the interstage coupling is 4 seconds, rendering the pre-amplifier suitable for studying slow phenomena such as spinal cord root potentials, electrocardiograms, etc. The heater supply is 6 V, but the first stage heaters are connected in series so that each valve receives only 3. A low cathode temperature and hence low noise are thus o
. Electronic apparatus for biological research. Electronic apparatus and appliances; Biology -- Research. +60, lAOk 1 + 60 50k ^3Q <iM X" Mm EF37A. Output Figure are triode-connected and facilities are provided for gain balancing. The time constant of the interstage coupling is 4 seconds, rendering the pre-amplifier suitable for studying slow phenomena such as spinal cord root potentials, electrocardiograms, etc. The heater supply is 6 V, but the first stage heaters are connected in series so that each valve receives only 3. A low cathode temperature and hence low noise are thus obtained. DIRECT-COUPLED PRE-AMPLIFIERS As soon as the frequency response of amplifiers has to extend down to zero frequency there is an immediate increase in complication, which seems to be inevitable and makes it worth while to consider carefully before embarking upon it. There are three approaches, each dictated by the requirements. (1) ^Straightforward'' aniplifiers. These have been discussed in Part I and attention has been drawn to the necessity for distinct static balancing and gain balancing controls and to the existence of drift. (2) 'Carrier' amplifiers. These are not true direct-coupled amplifiers but behave as if they were. The input signal is converted into an alternating one ('chopped') at a fixed frequency which is much higher than the highest frequency to which the apparatus is to respond. The alternating voltage thus produced undergoes conventional capacitor-coupled amplification, fol- lowed by phase-sensitive rectification. If it is then passed through a low-pass 619. 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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