A three-stage gallium-arsenide field-effect transistor amplifier giving a noise temperature of 29 K (0.4 dB noise figure) at a physical temperature of 13 K is described. The amplifier utilises a novel modular construction with coaxial air-lines, sliding λ/4 transformers, and packaged NE13783 and MGF1403 FETs. Noise parameters of these devices at 300 K and 13 K are reported.