The elimination of background ""noise"" in sensitive amplifiers
L. F. Curtiss · Bureau of Standards Journal of Research · 1933
A study has been made of the problem of reducing the background "noise" in a high-gain resistance-capacity coupled pulse amplifier used for registering ioniza- tion of individual ionizing particles.It has been found that, even after due care has been taken to reduce disturbances in the first two stages, a great improvement can be effected by suitable modification of the final or output stage.This con- sists in using several output tubes, preferably pentodes, in parallel, and selecting an operating point on the characteristic curve such that small fluctuations in the voltage applied to the control grids produce practically no change in the plate current and yet all pulses which exceed these fluctuations in the desired direction are reproduced in the plate current.Although this arrangement involves some distortion of very small pulses, the gain in the legibility of the oscillograph record is sufficient to compensate for this slight disadvantage.The results obtainable under various conditions are illustrated by reproductions of oscillograph records.