A Low-Noise Amplifier

This paper describes an amplifier circuit which yields very low noise factor, consisting of a grounded-cathode triode followed by a grounded-grid triode. The combination is entirely noncritical and provides the low noise factor of a triode with the high amplification and stability of a pentode. Noise factors averaging 0.25 db at a carrier frequency of 6 Mc. and 1.35 db at 30 Mc. have been achieved. Typical circuit details are given.