A tube is described which is based on the principle of interaction between a traveling electric field and an electron beam traveling at about the same velocity. Experiments on the interaction and the construction of a tube run as a sensitive amplifier at a wavelength of 9.1 centimeters are given. A noise factor of 11 decibels with a power amplification of 14 were obtained with one particular tube. An investigation of the field obtaining in a helix-the structure used for slowing down the wave-is briefly described, and the main results of an approximate theory of the tube are given.