Abstract
In a preliminary experiment under Avertin anesthetic the Wever-Bray experiment was repeated and their findings verified. The apparatus was an ordinary audio-frequency amplifier with head phones. The need for a more accurate record of the impulses from the nervous system was apparent. We first turned our attention to improvements in the amplifier. It was necessary to obtain a maximum of amplification with a minimum number of tubes. To meet this requirement we selected a resistance coupled circuit employing 2 four element type‘24 tubes, in the first 2 stages and one type‘47 pentode tube as an output. The screen potential of the second tube was varied by a wire potentiometer as a control of amplification. To prevent power loss on the output an output transformer suitable for the pentode was used.
For making permanent records a Westinghouse multi-element moving coil type oscillograph offered most promise of flexibility. The secondary of the output transformer was selected to match the “super-sensitive” strings of the oscillograph. These strings have a sensitivity of approximately .002 ampere per inch deflection with a resistance of 8 ohms. The oscillograph is supplied with 2 of these elements and 2 “standard” elements which may be used for timing or other purposes. Two of the above amplifiers were constructed and checked to make certain that they gave very nearly identical curves on the 2 super-sensitive oscillograph strings. The completed set up affords an undistorted output from below 80 to more than 10,000 cycles, and in the range from 80 to 1000 cycles an input potential of 50 micro-volts will give an output deflection of one centimeter with a quite steady base line and a sufficiently flat response. One amplifier and string were used for the electrical changes from the ear and the other was attached to a microphone pickup so that sounds could be photographed simultaneously from microphone and preparation.
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