Bioelectric-Research Apparatus

This paper describes a complete amplifying and cathode-ray-tube system suitable for certain bioelectric-research applications. Three independent amplifying channels, working into a three-trace cathode-ray tube allow the recording of three, independent, simultaneous phenomena. The three traces may be partially or wholly superimposed as desired. Each amplifying channel consists of a battery-operated, three-stage, direct-current amplifier coupled to a power-line-operated, direct-current output stage. All channels operate from a common battery and power-line supply. Cathode-ray-tube sweep circuits are direct-current-coupled and entirely power-line-operated. Individual control of centering and sweep speed for each trace is provided. An associated stimulating circuit, synchronized with the sweep, provides stimuli for biologic specimens under study. The amplifier input is either single-ended or differential as desired. Response is flat within 1 decibel from 0 to 7000 cycles per second with a maximum voltage gain of 131 decibels. A maximum voltage gain of 125 decibels may be attained with a response flat within 1 decibel from 0 to 14,000 cycles per second. The sweep amplifiers provide an undistorted output of approximately 500 volts, sufficient for full-scale deflection of the Western Electric 330C cathode-ray tube operating at 3 kilovolts accelerating voltage. Sweep frequencies range from 1 per minute to 20,000 per second.