Summary form only given. Microwave Technologies Inc. has begun the development of a compact nanotube-driven X-band microwave amplifier (NDXA). The NDXA is a compact vacuum tube that uses a rugged carbon-nanotube cold-cathode and a compact two-cavity system to produce X-band microwave radiation with very high-efficiency, making the NDXA ideal for airborne applications. We will present design considerations for an 8.4 GHz, 500-watt amplifier prototype. The NDXA should be capable of replacing conventional traveling-wave tubes in future radar and communication systems by offering substantial improvements in size, weight, and, especially efficiency over its counterparts