A method is presented in this paper for realizing tunable amplifiers with bandwidths of less than 0.5%; without the use of superconductors and cryogenic cooling. This method uses a small signal varactor up-converter to achieve these ultra narrow bandwidths. The equivalent circuit for the up-converter is presented as well as the circuit configuration of the narrow band negative resistance amplifier. The design and experimental results are presented for a 0.5% bandwidth negative resistance amplifier at 800 MHz; using this unique circuit design. These devices and circuits can be used for electronic warfare applications such as surveillance, electronic reconnaissance, jamming and frequency hopping. By Dr. Alfred I. Grayzel, Dr. Ashok (Ash) K. Gorwara, Paul Kuhn, Planar Monolithics Industries, Inc.